A device and method for measuring the distance between stacked wafers

Abstract

This invention belongs to the field of wafer inspection and relates to a distance measurement device and method for the gap between stacked wafers. The measurement device includes a light source beam splitter, a Y-axis displacement stage, a reflector, a Z-axis displacement stage, and a prism. The light source beam splitter connects a reference optical path and a measurement optical path. The reference optical path is located in the direction of the reflected light path of the light source beam splitter, and the measurement optical path is located in the direction of the transmitted light path of the light source beam splitter. A Y-axis displacement stage is disposed on the reference optical path, and a reflector is mounted on the Y-axis displacement stage. The reflector reflects the light source on the reference optical path into the light source beam splitter. A Z-axis displacement stage is disposed on the measurement optical path, and a prism is mounted on the Z-axis displacement stage. The prism reflects the light source on the measurement optical path onto the wafer and reflects the reflected light from the wafer into the light source beam splitter.

Description

Technical Field

[0001] This invention belongs to the technical field of wafer inspection, and more specifically, relates to a distance measuring device and method for measuring the gap between stacked wafers. Background Technology

[0002] As Moore's Law, the traditional method for predicting technological advancements, gradually comes to an end, chips are increasingly shifting towards 3D to continuously improve the performance and computing speed of semiconductor devices.

[0003] Novel micro-assembly technologies such as 3D stacking have the characteristics of high integration, light weight, small package size and low manufacturing cost. They will become an important means of increasing the density of chip transistors in the short term and have broad application prospects in the development of miniaturization, high density, high reliability and low power consumption of electronic products.

[0004] 3D stacking technology is a three-dimensional stacking processing technology that combines wafers, chips, or structures with different functions through stacking technology or micromachining technology such as via interconnects, to form three-dimensional integration, signal connectivity, and packaging at the wafer level, chip level, and silicon cap level in the Z-axis direction.

[0005] As the number of stacked wafer layers increases and environmental stresses become more severe, warping and bending of stacked wafers become more pronounced, significantly impacting device performance. Therefore, accurate measurement of the wafer spacing is crucial for real-time monitoring of device deformation and prediction of device lifespan. However, the wafer spacing typically ranges from hundreds of micrometers to millimeters, making it difficult for conventional sensors to measure such minute gaps. A high-precision, high-efficiency measurement device and method are urgently needed to solve the challenge of measuring wafer gaps.

[0006] Currently, optical measurement methods for wafers mainly focus on three-dimensional morphology measurement and surface defect detection. For gap measurement, probe discharge measurement is generally used. The probe discharge measurement method relies on clicking to move a probe with an applied DC voltage radially. The difference between the probe's travel distance and the initial installation gap is the gap distance. This method can measure very large gaps and is suitable for conductive materials. However, for nanoscale measurements of the gaps between stacked wafers, ranging from tens of micrometers to millimeters, existing conventional detection methods lack sufficient capability.

[0007] Therefore, it is necessary to develop a measurement system that can accurately detect the gap distance between stacked wafers, and to perform high-efficiency and high-precision measurement and evaluation of the gap distance between stacked wafers. This will help to detect changes in the gap distance between stacked wafers in a timely manner, predict the performance and lifespan of devices, and improve the utilization efficiency of devices. Summary of the Invention

[0008] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a measuring device and method for measuring the gap between stacked wafers. The device uses a prism to reflect the light source in the measurement optical path onto the wafer, and then reflects the reflected light from the wafer back into a light source beam splitter. By adjusting the Y-axis displacement stage in the reference optical path to change the optical path, an interference pattern containing wafer gap distance information is acquired through an observation camera. The interference pattern can be demodulated using computer program control of the Y-axis displacement stage and camera to obtain the measurement information of the stacked wafer gap. The measuring device of this invention can achieve the measurement of stacked wafer gaps from tens of micrometers to several millimeters. The measurement method based on this device, which uses computer program control of the displacement stage and camera to capture interference images, facilitates the efficient and high-precision measurement and evaluation of the gap between stacked wafers.

[0009] A first aspect of the present invention provides a measuring device for the gap between stacked wafers, comprising: a light source beam splitter, a Y-axis displacement stage, a reflector, a Z-axis displacement stage, and a prism;

[0010] The light source beam splitter is used to connect the reference optical path and the measurement optical path; wherein, the reference optical path is located in the direction of the reflected optical path of the light source beam splitter, and the measurement optical path is located in the direction of the transmitted optical path of the light source beam splitter;

[0011] The reference optical path is provided with a Y-axis displacement stage, and the reflector is mounted on the Y-axis displacement stage; wherein, the reflector is used to reflect the light source on the reference optical path into the light source beam splitter;

[0012] The measurement optical path is provided with the Z-axis displacement stage, and the Z-axis displacement stage is equipped with the prism; wherein, the prism is used to reflect the light source on the measurement optical path onto the wafer, and to reflect the reflected light on the wafer into the light source beam splitter.

[0013] As a preferred embodiment of the present invention, the prism is a reflective prism, and the size of the prism is 10-200 μm.

[0014] As a preferred embodiment of the present invention, the prism is made of photoresist silicon oxide material and is manufactured using a photolithography process.

[0015] As a preferred embodiment of the present invention, the measuring device further includes a three-axis displacement stage located on the measuring optical path for adjusting the spatial displacement on the measuring optical path.

[0016] As a preferred embodiment of the present invention, the measuring device further includes a light source, which is a parallel incoherent light source; preferably, the light source is white light.

[0017] As a preferred embodiment of the present invention, the measuring device further includes an observation camera, which is disposed in the opposite direction of the reference optical path.

[0018] As a preferred embodiment of the present invention, the reference optical path and the measurement optical path are arranged perpendicularly on a plane.

[0019] A second aspect of the invention provides a method for measuring the distance between stacked wafer gaps, the method comprising:

[0020] S1: Adjust the direction of the measuring optical path so that the light source in the measuring optical path is incident on the prism; adjust the direction in the reference optical path until an interference pattern is displayed on the observation camera;

[0021] S2: Adjust the displacement of the Y-axis displacement stage in the reference optical path to obtain the light intensity signal A of the interference pattern in the observation camera;

[0022] S3: Adjust the Z-axis displacement stage of the measurement optical path, and repeat step S2 to obtain the light intensity signal B of the interference pattern in the observation camera;

[0023] S4: Convert the light intensity signal A and the light intensity signal B into corresponding displacement data, and obtain the measurement result of the wafer gap based on the displacement data.

[0024] As a preferred embodiment of the present invention, in step S2, the displacement stroke of the Y-axis displacement stage is within 10 micrometers before and after the appearance of the interference pattern of the observation camera.

[0025] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0026] (1) This invention provides a measuring device capable of accurately detecting the gap distance between stacked wafers. The device utilizes a Z-axis displacement stage and a prism. The prism is mounted on the Z-axis displacement stage, allowing the device to reflect the light source in the measurement optical path onto the wafer, and then reflect the reflected light from the wafer into a light source beam splitter. The optical path is changed by adjusting the Y-axis displacement stage in the reference optical path, and an interference pattern containing wafer gap distance information is acquired in the observation camera. Furthermore, the optical path is converted by the displacement of the Z-axis displacement stage in the Z-axis direction, completing the measurement of adjacent wafers. Based on this measuring device, high-efficiency and high-precision measurement of the gap between stacked wafers can be achieved, enabling timely detection of changes in the gap distance between stacked wafers.

[0027] (2) When the prism in the measuring device of the present invention is a reflecting prism, the interference signal from the prism to the wafer can be measured through the reflection of the prism, especially when its size in any dimension is 10-200 μm. In particular, when the spacing between stacked wafers is generally several hundred micrometers to several millimeters, based on the micrometer size of the prism of the present invention, the distance information between the upper and lower wafers in the gap stacking direction can be accurately measured by the displacement of the Z-axis displacement stage, and then the gap information between adjacent wafers can be calculated.

[0028] (3) The prism of the present invention can be fabricated into a micron-sized prism using photolithography with photoresist silicon oxide material. Furthermore, based on the photolithography process, the quality and precision of the prism can be further guaranteed.

[0029] (4) The measuring device of the present invention includes a three-axis displacement stage, which is located in the X direction of the measuring optical path and does not interfere with the positional relationship of other components on the measuring optical path, and is used to adjust the position and direction of the measuring optical path. Therefore, especially when using the three-axis displacement stage during the device debugging stage, it is more convenient to fine-tune the position of the measuring optical path so that the light source coming out of the beam splitter can be aligned with the prism.

[0030] (5) The measuring device of the present invention uses an incoherent light source, which, compared with other light source measurements, ensures the measurement accuracy of the wafer gap based on the principle of incoherent light source interferometry. Incoherent light sources used in incoherent light source interferometry include, for example, deep ultraviolet LEDs, ultraviolet LEDs, monochromatic visible light LEDs, white light LEDs, and infrared LEDs. In particular, when white light is used, the obtained interference fringes are more pronounced.

[0031] (6) The measuring device of the present invention uses an observation camera, which is set in the opposite direction of the reference optical path, for receiving and displaying interference fringes.

[0032] (7) Based on the measuring device of the present invention, the measuring principle of the present invention is that the incoherent light emitted by the light source is split into two beams by a beam splitter. One beam is incident on the reference optical path, and the Y-axis displacement stage in the reference optical path is equipped with a reflector to reflect the beam. The other beam is incident on the measuring optical path, and the prism and wafer in the measuring optical path reflect the beam back. The reflected light in the reference optical path and the measuring optical path are split again by the beam splitter and finally form an observable interference pattern in the camera. The light source is turned on, and the displacement stage of the measuring optical path is adjusted so that the light source in the measuring optical path is incident on the prism. At the same time, the displacement of the Y-axis displacement stage of the reference optical path is adjusted and the light reflected from the measuring optical path forms an interference pattern on the camera. The Y-axis displacement stage of the reference optical path and the observation camera are controlled by a computer program. When the Y-axis displacement stage moves slowly and uniformly, the interference light intensity of the observation camera is measured at regular intervals. The wafer gap is monitored and observed by measuring the change in interference light intensity. The control of all components can be completed by the computer. The light intensity data is converted into corresponding displacement data, and the wafer gap measurement result is obtained by analyzing and evaluating the displacement data.

[0033] Stacked wafers are non-conductive and have very small gaps, typically ranging from hundreds of micrometers to millimeters. Existing gap measurements mainly rely on mechanical probes for conductivity measurement, which is very limited in application scenarios. The method of this invention is based on optical measurement principles. It uses a prism to collect reflected light data from the upper and lower wafers to measure the gap between adjacent wafers. This method offers high accuracy and wide applicability.

[0034] (8) Based on the measurement method of the present invention, the displacement stroke of the Y-axis displacement stage is preferably within 10 micrometers before and after the appearance of the interference pattern in the camera, which can accurately obtain the strongest interference signal within a gap distance. During the displacement process of the Y-axis displacement stage, if the displacement stroke is too large, interference fringes will not appear, increasing the measurement cost; if the displacement stroke is too large, the measurement will be inaccurate.

[0035] In summary, the measuring device of this invention can achieve high-efficiency and high-precision nanoscale measurement of the gap between stacked wafers from tens of micrometers to several millimeters. The measurement method based on this device uses computer program to control the displacement stage and the camera to capture interferometric images, which helps to measure and evaluate the gap between stacked wafers with high efficiency and high precision. It fills the gap in the existing technology field for measuring the gap between stacked wafers at the micrometer level and has great significance in predicting the performance and life of wafer devices and improving the efficiency of device use. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the device for measuring the gap between stacked wafers provided in an embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of the measurement optical path and the beam propagation principle between adjacent wafers provided by the present invention;

[0038] Figure 3 This is the interference pattern formed by the reference optical path and the measurement optical path at the camera in Example 1 of the present invention;

[0039] Figure 4 This is a flowchart of the stacked wafer gap measurement method provided in Example 1 of the present invention;

[0040] Figure 5 This is a graph showing the measurement results of the stacked wafer gap provided in Example 1 of the present invention.

[0041] Reference numerals: 1. Light source; 2. Beam splitter; 3. Y-axis stage; 4. Mirror; 5. Reference optical path; 6. Observation camera; 7. Z-axis stage; 8. Prism; 9. Triaxial stage; 10. Measurement optical path; 11. Wafer box. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0043] Figure 1 The schematic diagram illustrates a measuring device for the gap between stacked wafers provided by the present invention. The measuring device includes: a light source beam splitter, a Y-axis displacement stage, a reflector, a Z-axis displacement stage, a prism, a triaxial displacement stage, and an observation camera.

[0044] The reference optical path is connected to the reflected optical path of the beam splitter, and a Y-axis displacement stage and a reflector are provided on the reference optical path; the reflector is mounted on the Y-axis displacement stage.

[0045] The direction of the transmitted light path connected to the beam splitter is measured. The measured light path includes a prism and a Z-axis displacement stage; the prism is mounted on the Z-axis displacement stage.

[0046] Furthermore, the prism is a reflecting prism, and the size of the prism in any dimension is 10-200um.

[0047] Furthermore, the prism is fabricated from a photoresist silicon oxide material using a photolithography process. Alternatively, similar fabrication steps can be used to obtain a prism with a photolithographic microstructure.

[0048] Furthermore, in Figure 1 The device also includes a three-axis displacement stage located in the X direction of the measurement optical path, housing various components along the measurement optical path, including the Z-axis displacement stage. Alternatively, in the design of the actual device, a structure with the same function can be used as a substitute, allowing the light source exiting the beam splitter to be aligned with the prism.

[0049] Furthermore, in this invention, the light source is a parallel, incoherent light source, or it may include multiple incoherent light sources and multiple lenses adjusted to produce parallel light. In the embodiments of this invention, white light is preferred as an example.

[0050] exist Figure 1 An observation camera is also provided, positioned in the negative Y direction relative to the light source beam splitter. In actual testing, the device also includes a controller and a processing terminal; one end of the controller is connected to a three-axis displacement stage, and the other end is connected to the processing terminal.

[0051] exist Figure 1 The measuring device also features a light-shielding enclosure that surrounds all components outside the wafer box, preventing external light from affecting the measurement results.

[0052] exist Figure 1 It also includes a wafer box, in which the wafer to be tested is placed when testing the wafer.

[0053] The wafer gap is measured using the aforementioned measuring device. The specific measurement optical path and beam propagation between wafers in the wafer box are as follows: Figure 2 The prism is placed on the Z-axis displacement stage and moves along the Z-axis. The light beam passes through the prism into the wafer box, and then the emitted light returns to the beam splitter. Adjusting the Z-axis displacement stage allows the light beam to be directed to different positions in the wafer box until the incident light source is on the wafer.

[0054] It should be noted that the prism is a specially shaped prism with micron-sized dimensions, fabricated from photoresist silicon oxide material using photolithography. The optical path is converted by displacement along the Z-axis using a Z-axis displacement stage. The prism's actual design dimensions can be modified as needed, with dimensions ranging from 10-200 μm in any dimension, facilitating system setup. The prism fabrication steps are as follows:

[0055] Step (1): Remove impurities from the material surface. Clean the substrate with a certain amount of acetone for 5-10 minutes, then with a certain amount of isoacetone for 5-10 minutes, and finally with a certain amount of ethanol for 5-10 minutes. In actual preparation, it is only necessary to remove surface impurities.

[0056] Step (2): Spin coat a 50um-500um thick photoresist onto the substrate.

[0057] Step (3): Place the base on a baking machine and bake for 5-30 minutes.

[0058] Step (4): Use 300mJ / cm 2 -800mJ / cm 2 Exposure dose of ultraviolet light.

[0059] Step (5): Soak the substrate in alkaline developing solution for 5-10 minutes until the prism's specific size structure appears.

[0060] Step (6): Rinse with deionized water to remove any remaining liquid residue.

[0061] Step (7): Finally, dry with a nitrogen gun.

[0062] The specific implementation examples are as follows:

[0063] Example 1:

[0064] A distance measuring device for the gap between stacked wafers, the measuring device includes: a light source, a light source beam splitter, a Y-axis displacement stage, a reflector, a Z-axis displacement stage, a prism, a triaxial displacement stage, and an observation camera.

[0065] The optical path design and device structure design of implementation 1 are as follows: Figure 1 .

[0066] In Implementation 1, white light is selected as the light source.

[0067] The prism used in Implementation 1 follows the same manufacturing steps as the prism described above. Specifically, Implementation 1 uses a 100*100*100um cube prism.

[0068] This device measures the wafer gap by placing the wafer to be measured in a wafer box. For example... Figure 4 As shown, the specific method for measuring the distance between stacked wafers is as follows:

[0069] Step (1): Stack the wafers to be tested in a wafer box.

[0070] Step (2): Turn on the light source. The incoherent light emitted by the light source is split into two beams by the beam splitter. One beam is incident on the reference light path and the other beam is incident on the measurement light path.

[0071] Step (3): Adjust the three-axis displacement stage so that the light source in the measurement optical path is incident on the prism; adjust the Y-axis displacement stage in the reference optical path until an alternating bright and dark interference pattern can be seen on the observation camera. Finally, an interference pattern like this will be formed in the camera. Figure 3 The interference fringe pattern shown contains information about the wafer gap distance and can be observed.

[0072] Step (4): Use the computer program in the processing terminal to control the operation of the Y-axis displacement stage and the observation camera. While the Y-axis displacement stage is moving, record the light intensity of the interference pattern in the observation camera according to a certain pattern. The displacement stroke of the Y-axis displacement stage is within 10 micrometers before and after the appearance of the interference pattern in the observation camera.

[0073] Step (5): Adjust the Z-axis displacement stage under the prism to change the beam direction in the measurement optical path, and repeat step (4).

[0074] Step (6): Record the light intensity data; convert the light intensity data into corresponding displacement data; analyze the distance information from the prism to one of the wafers in the light intensity data to obtain the measurement result of the wafer gap.

[0075] Step (7): Turn off the light source and end the measurement.

[0076] like Figure 5 The test results are for the example implementation. Figure 5 The relationship between wafer gap measurement results and interference pattern light intensity was demonstrated. The distances from the prism to two adjacent wafers were measured using the aforementioned measurement method, and these two sets of data were superimposed to form... Figure 5 The wafer gap information data shown is as follows, where the wafer gap corresponding to the maximum interference light intensity is the actual wafer gap data.

[0077] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A distance measuring device for the gap between stacked wafers, characterized in that, The measuring device includes: a light source beam splitter (2), a Y-axis displacement stage (3), a reflector (4), an observation camera (6), a Z-axis displacement stage (7), and a prism (8); The light source beam splitter (2) is used to connect the reference optical path and the measurement optical path. The incoherent light emitted by the light source is split into two beams by the light source beam splitter (2). One beam is incident on the reference optical path and the other beam is incident on the measurement optical path. The reference optical path is located in the direction of the reflected optical path of the light source beam splitter, and the measurement optical path is located in the direction of the transmitted optical path of the light source beam splitter. The reference optical path and the measurement optical path are arranged perpendicularly on a plane. The reference optical path is provided with the Y-axis displacement stage (3), and the Y-axis displacement stage (3) is equipped with the reflector (4); wherein, the reflector is used to reflect the light source on the reference optical path to the light source beam splitter; The measurement optical path is provided with the Z-axis displacement stage (7), which is displaced in the Z direction. The Z-axis displacement stage (7) is mounted on the Z-axis displacement stage (7) and is displaced in the Z direction with the displacement stage. The prism is used to reflect the light source in the measurement optical path onto the wafer and to reflect the reflected light on the wafer into the light source beam splitter. By the displacement of the Z-axis displacement stage in the gap stacking direction, the distance information between the upper and lower wafers in adjacent wafers can be accurately measured, and the gap information between adjacent wafers can be calculated. The observation camera is positioned in the opposite direction of the reference optical path. The reflected light from the reference optical path and the measurement optical path passes through a beam splitter and ultimately forms interference fringes in the observation camera.

2. The distance measuring device for the gap between stacked wafers according to claim 1, characterized in that, The prism is a reflective prism, and the size of the prism is 10-200 μm.

3. The distance measuring device for the gap between stacked wafers according to claim 2, characterized in that, The prism is made of photoresist silicon oxide material and is fabricated using photolithography.

4. The distance measuring device for the gap between stacked wafers according to claim 1, characterized in that, The measuring device also includes a three-axis displacement stage (9) located on the measuring optical path for adjusting the spatial displacement on the measuring optical path.

5. The distance measuring device for the gap between stacked wafers according to claim 1, characterized in that, The measuring device also includes a light source (1), which is a parallel incoherent light source.

6. The distance measuring device for the gap between stacked wafers according to claim 5, characterized in that, The light source (1) is white light.

7. A method for measuring the distance between stacked wafers using the apparatus of any one of claims 1-5, characterized in that, The method includes: S1: Adjust the direction of the measurement optical path so that the light source in the measurement optical path is incident on the prism; adjust the direction in the reference optical path until an interference pattern with wafer gap distance information is displayed on the observation camera; S2: Adjust the displacement of the Y-axis displacement stage in the reference optical path to obtain the light intensity signal A of the interference pattern with wafer gap distance information in the observation camera; S3: Adjust the Z-axis displacement stage of the measurement optical path so that the light beam illuminates another wafer in the adjacent wafer, and repeat step S2 to obtain the light intensity signal B of the interference pattern in the observation camera; S4: Convert the light intensity signal A and the light intensity signal B into corresponding displacement data, and analyze and evaluate the displacement data to obtain the measurement result of the wafer gap.

8. The method for measuring the distance between stacked wafer gaps according to claim 6, characterized in that, In step S2, the displacement stroke of the Y-axis displacement stage is within 10 micrometers before and after the appearance of the interference pattern on the observation camera.

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