CN111599709B - Method for detecting wafer bonding interface defects and storage medium - Google Patents
Method for detecting wafer bonding interface defects and storage medium Download PDFInfo
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- CN111599709B CN111599709B CN202010482220.8A CN202010482220A CN111599709B CN 111599709 B CN111599709 B CN 111599709B CN 202010482220 A CN202010482220 A CN 202010482220A CN 111599709 B CN111599709 B CN 111599709B
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- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L22/00—Testing or measuring during manufacture or treatment; Reliability measurements, i.e. testing of parts without further processing to modify the parts as such; Structural arrangements therefor
- H01L22/10—Measuring as part of the manufacturing process
- H01L22/12—Measuring as part of the manufacturing process for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/04—Analysing solids
- G01N29/06—Visualisation of the interior, e.g. acoustic microscopy
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- G01N29/0681—Imaging by acoustic microscopy, e.g. scanning acoustic microscopy
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
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- G01N2291/028—Material parameters
- G01N2291/0289—Internal structure, e.g. defects, grain size, texture
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- G—PHYSICS
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- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/04—Wave modes and trajectories
- G01N2291/044—Internal reflections (echoes), e.g. on walls or defects
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/26—Scanned objects
- G01N2291/269—Various geometry objects
- G01N2291/2697—Wafer or (micro)electronic parts
Abstract
The invention provides a method for detecting defects of a wafer bonding interface and a storage medium, wherein the method for detecting the defects of the wafer bonding interface comprises the following steps: placing a bonded wafer at a scanning position, so that a bonding interface of the bonded wafer is positioned in a detection threshold window, and a metal layer of the bonded wafer is positioned in a reference threshold window; scanning a detection threshold window to collect an echo signal of the detection threshold window, and taking the echo signal of the detection threshold window as a detection signal; scanning a reference threshold window to collect echo signals of the reference threshold window, and taking the echo signals of the reference threshold window as reference signals; and carrying out logical operation on the detection signal and the reference signal to obtain a difference signal. By the arrangement, the problems of repeated importing and establishing of the graphic information are avoided, and the detection efficiency is improved; the detection sensitivity of the detection program is improved, and the condition of missing detection caused by directly filtering out the void defect signal is avoided.
Description
Technical Field
The invention relates to the technical field of integrated circuit manufacturing, in particular to a method for detecting defects of a wafer bonding interface and a storage medium.
Background
With the development of semiconductor technology, Back Side Illumination (BSI) image sensors are widely used in various fields. The backside-illuminated (BSI) image sensor manufacturing technology is a manufacturing technology for thinning a wafer backside of a Complementary Metal-Oxide-Semiconductor (CMOS) image sensor and building an optical filter and a microlens on the backside. Because the thinning process of the back of the wafer is to process the wafer silicon wafer with the original thickness of 775 microns to a semiconductor epitaxial layer (EPI) with the thickness of only about a few microns, the wafer of a CMOS Image Sensor (CIS) and the wafer carrying wafer need to be bonded together to form a bonded wafer before thinning, and then subsequent processing can be carried out. The wafer bonding technology is that two mirror polished homogeneous or heterogeneous wafers are tightly combined through chemical and physical actions, and after the wafers are combined, atoms on an interface are acted by external force to react to form covalent bonds to be combined into a whole, so that the combined interface achieves specific bonding strength. The specific wafer bonding process comprises the following steps: firstly, fusion bonding is carried out between silicon oxide layers through low-temperature plasma, and then Van der Waals force between bonding layers is converted into a covalent bond through high-temperature annealing treatment, so that high-strength wafer bonding is completed. Parameters characterizing the quality of the bonded wafer include the magnitude of the bonding force and the presence or absence of void defects.
Void defects inside the bonded wafer are typically detected using an ultrasonic scanning microscope. The detection principle of the ultrasonic scanning microscope is to utilize the characteristic that ultrasonic waves can be well directionally propagated in an elastic medium, and the interaction between the acoustic waves and the elastic medium of a tiny sample can be accurately reflected. When the surface wave (echo signal of the first reflection after the ultrasonic wave meets the bonded wafer) meets the cavity or the interface existing in the bonded wafer, a significant difference occurs in the propagation property, and the defect information and the material information in the bonded wafer can be clearly understood by collecting the echo signals. In practical application, the echo signals of all the points in the wafer bonding interface are scanned and collected to draw a detection image of plane scanning, and the echo signals in a specific depth range can be intercepted by arranging a single threshold window so as to meet the detection requirement. Typically, the threshold window is set to include the echo signal on the detection interface within the clipping range.
The problem of noise signals is generally existed in the detection of a wafer bonding interface, and the noise signals are caused by a plurality of reasons, wherein one main reason is the noise signals caused by a metal interconnection layer near the bonding interface, when ultrasonic waves pass through an interface of heterogeneous materials such as metal and silicide media, reflection signals are generated, and if the time position of the reflection signals is within a set threshold window range, the reflection signals are contained in the echo signals and received and calculated by a receiver. In general, reducing the range of the threshold window can effectively reduce the reflected signal of the metal interconnection layer received in the threshold, but if the threshold window is set too small, the hole defect signal of the bonding interface to be detected may be excluded from the detection range, thereby causing a detection omission risk. Therefore, under the condition of ensuring a threshold window with a certain width, noise signals caused by the metal interconnection layer are inevitable.
The method for filtering wafer bonding interface noise signals adopted by the prior art comprises the following steps: before scanning, the graphic information of the metal interconnection layer is input and stored in the calculation software of the detection result, after scanning is finished, the detection result is compared with the graphic information, and signals with the graphic information are directly filtered and are not included in the calculation result. However, the conventional method has the following problems:
1. when detecting a new wafer key interface, the graphic information of the metal interconnection layer needs to be imported and established again, and the program establishing efficiency is low.
2. Under the condition that the area of a noise signal graph of a metal interconnection layer of a wafer bonding interface is large, a signal at the position is directly filtered and is not included in the calculation of a detection result, and if a cavity defect exists at the position, the signal of the cavity defect can be directly filtered, so that the detection missing risk is caused.
Therefore, how to accurately and efficiently detect the defect of the wafer bonding interface, and further avoid the problem of low detection efficiency caused by low program building efficiency and the problem of missing detection of void defect information is a problem that needs to be solved at present.
Disclosure of Invention
The invention aims to provide a method for detecting defects of a wafer bonding interface and a storage medium, which are used for solving the problems of low program establishing efficiency and low detection efficiency caused by repeatedly importing and establishing graphic information and the problem of missed detection caused by directly filtering out void defect signals.
In order to solve the above technical problem, the present invention provides a method for detecting a defect of a wafer bonding interface, which comprises the following steps: providing a bonded wafer, wherein the bonded wafer comprises a bonding interface; placing the bonded wafer at a scanning position, so that a bonding interface of the bonded wafer is positioned in a detection threshold window, and a metal layer of the bonded wafer is positioned in a reference threshold window; scanning a detection threshold window to collect an echo signal of the detection threshold window, and taking the echo signal of the detection threshold window as a detection signal; scanning a reference threshold window to collect echo signals of the reference threshold window, and taking the echo signals of the reference threshold window as reference signals; obtaining a difference signal by performing logical operation on the detection signal and the reference signal; and judging the defect result of the bonding interface according to the difference signal.
Optionally, the number of the reference threshold windows is at least one.
Optionally, the reference threshold window and the detection threshold window have an overlapping portion but do not completely overlap, and the reference threshold window and the detection threshold window overlap in the thickness direction of the bonded wafer.
Optionally, the reference threshold window includes a metal interconnection layer of the bonded wafer.
Optionally, the reference threshold window does not include the bonding interface.
Optionally, the step of obtaining a difference signal by performing a logical operation on the detection signal and the reference signal includes: determining a gain factor based on a predetermined logical operation formula, determining the difference signal based on the gain factor in combination with the logical operation formula.
Optionally, the method for determining the gain factor based on the predetermined logical operation formula includes: providing the predetermined logical operation formula, wherein the predetermined logical operation formula is as follows:
wherein, anRepresenting the nth predetermined gain factor; xnRepresents the nth of said reference signals; y represents the detection signal; z represents the difference signal; determining at least one preset gain coefficient, and bringing the at least one preset gain coefficient into the preset logical operation formula to obtain at least one calculation result; calculating the at least oneAnd determining a preset gain coefficient corresponding to the calculation result with the maximum signal-to-noise ratio as the gain coefficient.
Optionally, the method for determining the difference signal based on the gain factor and in combination with the logical operation formula includes: the gain coefficient is brought into a logical operation formula, and the obtained result is determined as a difference signal; the logical operation formula is as follows:
wherein, bnRepresents the nth gain factor; xnRepresents the nth of said reference signals; y represents the detection signal; z represents the difference signal.
Optionally, before the step of providing a wafer bonding structure, the method for detecting the wafer bonding interface defect includes: presetting a threshold value of the difference signal; the step of judging the defect result of the wafer bonding interface through the difference signal comprises the following steps: and comparing the difference signal with the threshold value to judge the defect result.
The invention also provides a storage medium, wherein the storage medium is stored with a computer program, and when the computer program is executed, the method for detecting the wafer bonding interface defects can be realized.
The invention provides a method for detecting defects of a wafer bonding interface and a storage medium of defect signals, wherein the method for detecting the defects of the wafer bonding interface comprises the following steps: providing a bonded wafer, wherein the bonded wafer comprises a bonding interface; placing the bonded wafer at a scanning position, so that a bonding interface of the bonded wafer is positioned in a detection threshold window, and a metal layer of the bonded wafer is positioned in a reference threshold window; scanning a detection threshold window to collect an echo signal of the detection threshold window, and taking the echo signal of the detection threshold window as a detection signal; scanning a reference threshold window to collect echo signals of the reference threshold window, and taking the echo signals of the reference threshold window as reference signals; obtaining a difference signal by performing logical operation on the detection signal and the reference signal; and judging the defect result of the bonding interface according to the difference signal. According to the arrangement, the echo signals are collected through the reference threshold window to obtain the reference signals, so that the problems of repeated introduction and graph information establishment are avoided, the program establishment efficiency is improved, and the detection efficiency is further improved; the signal-to-noise ratio of the defect distribution diagram of the difference signal obtained by logical operation of the detection signal and the reference signal to the void defect of the bonding interface is high, so that the detection sensitivity of the detection program is improved, and the condition that the void defect signal is directly filtered to cause missing detection is avoided.
Drawings
It will be appreciated by those skilled in the art that the drawings are provided for a better understanding of the invention and do not constitute any limitation to the scope of the invention. Wherein:
FIG. 1 is a flowchart illustrating a method for detecting defects in a wafer bonding interface according to an embodiment of the present invention;
FIG. 2 is a scanning plane of a method for detecting defects of a wafer bonding interface according to an embodiment of the present invention;
FIG. 3 is a scanned image of a reference signal in a method for detecting defects in a wafer bonding interface according to an embodiment of the present invention;
FIG. 4 is a scanned image of a detection signal in a method for detecting a defect in a wafer bonding interface according to an embodiment of the present invention;
fig. 5 is a scanned image of a difference signal in a method for detecting a wafer bonding interface defect according to an embodiment of the present invention.
In the drawings:
10-bond wafer, 10' -device wafer, 11-metal layer, 12-silicon substrate layer;
20-bonding interface;
30-scanned image of void defect signal;
40-a scanned image of the noise signal;
50-a scanned image of a wafer slice position;
100-detection threshold window; 200-reference threshold window.
Detailed Description
To further clarify the objects, advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is to be noted that the drawings are in greatly simplified form and are not to scale, but are merely intended to facilitate and clarify the explanation of the embodiments of the present invention. Further, the structures illustrated in the drawings are often part of actual structures. In particular, the drawings may have different emphasis points and may sometimes be scaled differently.
As used in this specification, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise. As used in this specification, the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise.
The invention provides a method for detecting defects of a wafer bonding interface, which is characterized in that a reference threshold window is added and used for collecting reference signals, and the reference signals and detection signals are subjected to logic operation to obtain difference signals, so that noise signals caused by non-void defects (metal interconnection layers) are filtered, and the detection sensitivity of a detection program is improved.
The invention provides a method for detecting defects of a wafer bonding interface and a storage medium, wherein the method for detecting the defects of the wafer bonding interface comprises the following steps: providing a bonded wafer, wherein the bonded wafer comprises a bonding interface; placing the bonded wafer at a scanning position, so that a bonding interface of the bonded wafer is positioned in a detection threshold window, and a metal layer of the bonded wafer is positioned in a reference threshold window; scanning a detection threshold window to collect an echo signal of the detection threshold window, and taking the echo signal of the detection threshold window as a detection signal; scanning a reference threshold window to collect echo signals of the reference threshold window, and taking the echo signals of the reference threshold window as reference signals; obtaining a difference signal by performing logical operation on the detection signal and the reference signal; and judging the defect result of the bonding interface according to the difference signal. According to the arrangement, the echo signals are collected through the reference threshold window to obtain the reference signals, so that the problems of repeated introduction and graph information establishment are avoided, the program establishment efficiency is improved, and the detection efficiency is further improved; the signal-to-noise ratio of the defect distribution diagram of the difference signal obtained by logical operation of the detection signal and the reference signal to the void defect of the bonding interface is high, so that the detection sensitivity of the detection program is improved, and the condition that the void defect signal is directly filtered to cause missing detection is avoided; furthermore, the method for detecting the wafer bonding interface defects can also ensure that the defect condition can still be effectively detected under the condition that wafer patterns exist near the bonding interface, particularly on ultra-thin stacking technology products, and can quickly improve the product yield.
The following description refers to the accompanying drawings.
FIG. 1 is a flowchart illustrating a method for detecting defects in a wafer bonding interface according to an embodiment of the present invention; FIG. 2 is a scanning plane of a method for detecting defects of a wafer bonding interface according to an embodiment of the present invention; FIG. 3 is a scanned image of a reference signal in a method for detecting defects in a wafer bonding interface according to an embodiment of the present invention; FIG. 4 is a scanned image of a detection signal in a method for detecting a defect in a wafer bonding interface according to an embodiment of the present invention; fig. 5 is a scanned image of a difference signal in a method for detecting a wafer bonding interface defect according to an embodiment of the present invention.
Referring to fig. 1 to fig. 2, the present embodiment provides a method for detecting a wafer bonding interface defect and a noise reduction device for a scanning signal, which are applied to detecting a wafer defect signal, and the method for detecting a wafer bonding interface defect includes the following steps:
s100: providing a bonded wafer 10, wherein the bonded wafer 10 includes a bonding interface 20;
s200: placing the bonded wafer 10 at a scanning position such that the bonding interface 20 of the bonded wafer 10 is within the detection threshold window 100 and the metal layer 11 of the bonded wafer 10 is within the reference threshold window 200;
s300: scanning a detection threshold window 100 to collect an echo signal of the detection threshold window 100, and taking the echo signal of the detection threshold window as a detection signal; scanning a reference threshold window 200 to obtain an echo signal of the reference threshold window 200, and using the echo signal of the reference threshold window 200 as a reference signal;
s400: obtaining a difference signal by performing logical operation on the detection signal and the reference signal;
s500: the defect result of the bonding interface 20 is judged by the difference signal.
In the method for detecting defects of a wafer bonding interface provided by this embodiment, one, two, or more reference threshold windows 200 are added on the basis of a detection method only including one detection threshold window 100 to detect a bonded wafer 10, and the reference threshold windows 200 are preferably located in a region near the reference threshold windows 200, specifically, the reference threshold windows include the metal layer 11 of the bonded wafer 10, and more preferably, the reference threshold windows do not include the bonding interface 20 of the bonded wafer 10, thereby avoiding the situation that the same signal is collected as the detection threshold window 100. And collecting the echo signal of the reference threshold window 200 through the reference threshold window 200 to obtain a reference signal, carrying out logical operation on the reference signal and the detection signal to obtain a difference signal, wherein a scanned image obtained through the difference signal is a final defect result. According to the arrangement, the reference threshold window 200 is added, the echo signal of the reference threshold window 200 is collected, logical operation can be performed through two different signals, a difference signal is obtained, the difference signal after the logical operation is based on the reference signal, noise signals caused by non-cavity defects (metal interconnection layers 13) in the detection signal are filtered, the signal to noise ratio of a defect distribution diagram obtained through the calculation of the difference signal to the cavity defects of the bonding interface 20 is higher, the detection sensitivity of a detection program is improved, the defect condition can be effectively detected under the condition that wafer patterns exist near the bonding interface 20, particularly on the bonding wafer of the ultrathin stack technology, and the yield of the bonding wafer 10 can be quickly improved.
It is to be understood that the reference threshold window 200 includes the metal layer 11 of the bonded wafer 10. When the bonded wafer 10 is scanned, the bonded wafer 10 is placed at a scanning position, and a scanning surface is directed to a machine scanning direction, where the scanning surface represents a surface of the bonded wafer 10 along a thickness direction, and is used for a detection threshold window 100 to scan a detection signal and a reference threshold window 200 to scan a reference signal. During scanning, the machine can scan the metal layer 11 on the scanning surface of the bonded wafer 10 through the reference threshold window 200; the number of the reference threshold windows 200 may be one or multiple, and multiple reference threshold windows 200 may have overlapping portions (may be incomplete overlapping, as long as there are overlapping portions), or may not overlap with each other, that is, there are no overlapping portions at all; the reference threshold window 200 may include the bonding interface 20, or may not include the bonding interface 20 and be located in the vicinity of the bonding interface 20. With such an arrangement, the reference threshold window 200 can collect the reference signal at any position of the metal layer 11 of the bonded wafer 10, and further perform a logic operation on the reference signal and the detection signal.
The detection threshold window 100 must include the bonding interface 20 of the bonded wafer 10, the size of the detection threshold window 100 is not limited, and the reference threshold window 200 and the detection threshold window 100 may overlap with each other (i.e., have a partial overlap or a complete overlap), or may not overlap with each other (i.e., have no overlap at all). In actual detection, the reference threshold window 200 and the detection threshold window 100 do not completely coincide, thereby avoiding invalid detection.
The bonded wafer 10 including the bonding interface 20 has various forms, one of which is a wafer provided with a metal interconnection layer 13 and a polished wafer, and the other is a wafer provided with an integrated circuit and the metal interconnection layer 13 for bonding, in this embodiment, as shown in fig. 2, two device wafers 10' including a metal layer 11 and a silicon substrate layer 12 are bonded to each other to form the bonding interface 20, wherein solid dark black rectangular frames both represent the metal interconnection layer 13. Of course, in other embodiments, the device wafer 10' and the carrier wafer may be bonded to each other to form the bonded wafer 10, and whatever bonding form is, as long as there is a bonding interface 20, as shown in fig. 2, between the upper limit (the upper dotted line in fig. 2) and the lower limit (the lower dotted line in fig. 2, where the upper and lower are the upper and lower directions in fig. 2) of the detection threshold window 100, the bonding interface 20 is included. The source of the noise signal is an interface reflection wave caused by a heterogeneous material interface, i.e., the metal interconnection layer 13, on the pattern in the bonded wafer 10. In the scanning process, the echo signal in the detection threshold window 100 has interface reflection waves from the metal interconnection layer 13 pattern in the bonded wafer 10, and the noise signal is large, so that the automatic calculation of the void defect result is influenced. The filtered difference signal is obtained by collecting the echo signal of the metal interconnection layer 13 in the reference threshold window 200, and then filtering the echo signal of the metal interconnection layer 13 in the detection signal through logic operation.
The number of reference threshold windows 200 is preferably at least one. In this embodiment, as shown in fig. 2, the number of the reference threshold windows 200 is one, and certainly, the number of the reference threshold windows 200 may be two or more, so that the scanning detection apparatus may collect more echo signals at different positions, and further, when calculating the difference signal, the difference signal may be more accurate. When the position of the detection threshold window 100 is different from the position of the reference threshold window 200, the windows at different positions are located at different phases of the echo signal, and the signal strength may be different, so that the reference threshold windows 200 need to be distributed near the detection threshold window 100 and adjacent to the detection threshold window 100. Therefore, it is preferable that the position of the reference threshold window 200 and the position of the detection threshold window 100 are set to overlap partially but not completely, and the reference threshold window 200 and the detection threshold window 100 overlap in the thickness direction of the bonded wafer 10 (the view in fig. 2 is a view showing the thickness of the bonded wafer 10). With continued reference to fig. 2, the reference threshold window 100 preferably does not include the bonding interface 20, so that the echo signal received by the reference threshold window 100 does not include an echo signal of a hole defect in the bonding interface 20, and thus the echo signal of the reference threshold window 200 is not affected by the hole defect signal.
Since the detection threshold window 100 and the reference threshold window 200 are adjacent to each other, but the signal strength may be significantly different at different phases of the echo signal, it is necessary to keep the signal strength of the reference threshold window 200 and the detection threshold window 100 as the same as possible. It is known to those skilled in the art that the change of the gain factor can adjust the intensity of the reference signal, and the change of the intensity of the reference signal can further affect the intensity of the difference signal and further affect the signal-to-noise ratio of the difference signal (in this embodiment, the signal-to-noise ratio refers to the ratio of the void defect signal to the non-void defect signal). When the signal-to-noise ratio of the difference signal is the maximum, the defect result obtained from the difference signal is the best, and the defect result of the bonding interface 20 can be further accurately judged. Therefore, in order to obtain a difference signal with a high signal-to-noise ratio, first, an appropriate gain coefficient needs to be determined, and the predetermined difference signal is obtained by substituting a plurality of predetermined gain coefficients into a predetermined logical operation formula, wherein the predetermined gain coefficients are numbers larger than zero, and preferably, the predetermined gain coefficients can be between 0 and 1. Then, calculating the signal-to-noise ratio of the predetermined difference signal, and determining the predetermined gain coefficient as the final gain coefficient when the signal-to-noise ratio of the predetermined difference signal corresponding to one predetermined gain coefficient is maximum. Therefore, preferably, the step of obtaining a difference signal by logically operating the detection signal and the reference signal comprises: determining a gain factor based on a predetermined logical operation formula, determining the difference signal based on the gain factor in combination with the logical operation formula.
The predetermined logical operation is preferably as follows: :
wherein, anRepresenting the nth predetermined gain factor; xnRepresents the nth of said reference signals; y represents the detection signal; z represents the difference signal. Determining at least one preset gain coefficient, and bringing the at least one preset gain coefficient into the preset logical operation formula to obtain at least one calculation result; and determining a preset gain coefficient corresponding to the calculation result with the maximum signal-to-noise ratio in the at least one calculation result as a gain coefficient.
After the gain coefficient is determined, the gain coefficient is brought into a logical operation formula, and the obtained result is determined as a difference signal; the logical operation formula is as follows:
wherein, bnRepresents the nth gain factor; xnRepresents the nth of said reference signals; y represents the detection signal; z represents the difference signal. In the exemplary embodiment, there is a reference threshold window 200, and a reference signal X is adjusted by a gain factor b and then subtracted from the reference signal to obtain a difference signal Z. In other embodiments, the number of the reference threshold windows 200 may be n, the n reference threshold windows 200 may collect corresponding reference signals, and the nth reference threshold window obtains the gained reference signal through the gain comprehensive adjustment of the nth gain coefficient.
Referring to fig. 3-5, fig. 3 is a scanned image of a reference signal X, fig. 4 is a scanned image of a detection signal Y, fig. 5 is a scanned image of a difference signal Z, a white portion of a non-circular irregular shape in a left white circle in fig. 3-5 is a scanned image 30 of a hole defect signal, a regular circular portion in the white portion is a scanned image 50 of a trimming position of a bonded wafer 10, and a periodic pattern of black and gray on a right side is a scanned image 40 of a noise signal. It can be seen from the scanned graph that the intensity of the noise signal of the detection signal Y is strong, the detection signal Y performs logical operation with the reference signal X to obtain the difference signal Z, and the noise signal intensity of the difference signal Z is obviously weakened, which indicates that after the reference threshold window 200 is added, the detection precision of the difference signal Z processed by the reference signal X is obviously improved, and the noise reduction effect is obvious.
Specifically, the detection signal and the reference signal are obtained by ultrasonic scanning. In the present exemplary embodiment, the detection signal and the reference signal are detected by an ultrasonic scanning microscope. The ultrasonic scanning microscope detection utilizes the characteristic that ultrasonic waves can be well directionally propagated in an elastic medium, the interaction between sound waves and the elastic medium of a tiny sample can be accurately reflected, and detection signals and reference signals can be collected with high precision and high sensitivity. Similarly, the main noise source of ultrasonic wafer scanning is interface reflection waves caused by a heterogeneous material interface on a pattern in the bonded wafer 10, and the noise signal in ultrasonic inspection of the bonded wafer 10 is a signal component higher than the background level caused by a non-void defect included in the captured echo signal.
In the ultra-thin stack technology bonded wafer 10, the slide glass above the bonding interface 20 is replaced by a logic wafer with integrated circuits, when ultrasonic waves pass through the logic wafer and reach the bonding interface 20, the propagation conditions of the ultrasonic waves at each plane position are greatly different due to pattern differences, and a detection signal is caused to have interface reflection waves from the patterns of the metal interconnection layers 13 in the logic wafer, and the non-cavity defect echo signal component in the detection signal is filtered through the combination calculation of a reference signal and the detection signal. Because the propagation speed of sound waves in a solid is high, and the length of the metal interconnection layer 13 from the bonding interface 20 is small, an ultrasonic transducer with higher frequency and a transmitter with shorter pulse width need to be adopted in a matching manner, and the setting precision of threshold time is further improved, so that a better noise reduction effect is achieved.
Preferably, before the step of setting the position of the detection threshold window 100, the method for detecting the wafer bonding interface defect includes: presetting a threshold value of the difference signal; the step of judging the defect result through the difference signal comprises the following steps: and comparing the difference signal with the threshold value to judge the defect result.
A storage medium for wafer bonding interface defect signals, the storage medium having a computer program stored thereon, the computer program being capable of implementing the method for detecting wafer bonding interface defects as described above when executed. Specifically, the storage medium stores the defect result, when the defect signal of the bonded wafer 10 needs to be detected, an operator only needs to select the option of the storage medium and store the detection result into the storage medium, so that the defect signal filtered by the reference signal can be obtained. The storage medium for the wafer bonding interface defect signal has the beneficial effects brought by the detection method for the wafer bonding interface defects, and details are not repeated here. The principle of other components of the storage medium for wafer bonding interface defect signals can be referred to the prior art, and will not be described herein.
In summary, in the method for detecting a defect on a wafer bonding interface and the storage medium provided by the present invention, the method for detecting a defect on a wafer bonding interface includes the following steps: providing a bonded wafer, wherein the bonded wafer comprises a bonding interface; placing the bonded wafer at a scanning position, so that a bonding interface of the bonded wafer is positioned in a detection threshold window, and a metal layer of the bonded wafer is positioned in a reference threshold window; scanning a detection threshold window to collect an echo signal of the detection threshold window, and taking the echo signal of the detection threshold window as a detection signal; scanning a reference threshold window to collect echo signals of the reference threshold window, and taking the echo signals of the reference threshold window as reference signals; obtaining a difference signal by performing logical operation on the detection signal and the reference signal; and judging the defect result of the bonding interface according to the difference signal. According to the arrangement, the echo signals are collected through the reference threshold window to obtain the reference signals, so that the problems of repeated introduction and graph information establishment are avoided, the program establishment efficiency is improved, and the detection efficiency is further improved; the signal-to-noise ratio of the defect distribution diagram of the difference signal obtained by logical operation of the detection signal and the reference signal to the void defect of the bonding interface is high, so that the detection sensitivity of the detection program is improved, and the condition that the void defect signal is directly filtered to cause missing detection is avoided. Furthermore, the method for detecting the wafer bonding interface defects provided by the invention can also ensure that the defect condition can be effectively detected under the condition that wafer patterns exist near the bonding interface, particularly on ultra-thin stacking technology products, and can quickly improve the product yield.
The above description is only for the purpose of describing the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention, and any variations and modifications made by those skilled in the art based on the above disclosure are within the scope of the appended claims.
Claims (9)
1. A method for detecting wafer bonding interface defects is characterized by comprising the following steps:
providing a bonded wafer, wherein the bonded wafer comprises a bonding interface;
placing the bonded wafer at a scanning position, so that a bonding interface of the bonded wafer is in a detection threshold window, and a metal layer of the bonded wafer is in a reference threshold window, wherein the reference threshold window does not contain the bonding interface;
scanning a detection threshold window to collect an echo signal of the detection threshold window, and taking the echo signal of the detection threshold window as a detection signal;
scanning a reference threshold window to collect echo signals of the reference threshold window, and taking the echo signals of the reference threshold window as reference signals;
obtaining a difference signal by performing logical operation on the detection signal and the reference signal;
and judging the defect result of the bonding interface according to the difference signal.
2. The method as claimed in claim 1, wherein the number of the reference threshold windows is at least one.
3. The method of claim 1, wherein the reference threshold window and the detection threshold window overlap partially but not completely, and the reference threshold window and the detection threshold window overlap in a thickness direction of the bonded wafer.
4. The method of claim 1, wherein the reference threshold window comprises a metal interconnect layer of the bonded wafer.
5. The method as claimed in claim 1, wherein the step of obtaining the difference signal by performing a logic operation on the detection signal and the reference signal comprises: determining a gain factor based on a predetermined logical operation formula, determining the difference signal based on the gain factor in combination with the logical operation formula.
6. The method as claimed in claim 5, wherein the step of determining the gain factor based on the predetermined logic operation formula comprises:
providing the predetermined logical operation formula, wherein the predetermined logical operation formula is as follows:
wherein, anRepresenting the nth predetermined gain factor; xnRepresents the nth of said reference signals; y represents the detection signal; z represents the difference signal;
determining at least one preset gain coefficient, and bringing the at least one preset gain coefficient into the preset logical operation formula to obtain at least one calculation result;
and determining a preset gain coefficient corresponding to the calculation result with the maximum signal-to-noise ratio in the at least one calculation result as a gain coefficient.
7. The method as claimed in claim 6, wherein the step of determining the difference signal based on the gain factor and the logic operation formula comprises:
the gain coefficient is brought into a logical operation formula, and the obtained result is determined as a difference signal; the logical operation formula is as follows:
wherein, bnRepresents the nth gain factor; xnRepresents the nth of said reference signals; y represents the detection signal; z represents the difference signal.
8. The method as claimed in claim 1, wherein before the step of providing a wafer bonding structure, the method comprises: presetting a threshold value of the difference signal; the step of judging the defect result of the wafer bonding interface through the difference signal comprises the following steps: and comparing the difference signal with the threshold value to judge the defect result.
9. A storage medium having a computer program stored thereon, wherein the computer program is capable of implementing the method for detecting wafer bonding interface defects according to any one of claims 1 to 8 when executed.
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