Alignment device for off-axis illumination, nanoimprint device and imprint alignment method

Abstract

The application discloses an off-axis illumination alignment device, a nano-imprint device and an imprint alignment method, and relates to the technical field of nano-imprint. The alignment device comprises: an illumination unit which provides multiple illumination lights respectively, and the illumination lights irradiate an alignment object in x and y directions respectively at a certain incident angle; and an imaging unit which is vertically arranged above the alignment object and obtains a moire fringe image representing the alignment degree between the alignment object and a template, wherein the first diffraction light and the second diffraction light are generated by the mark grating on the alignment object and the template grating on the template when the illumination light is incident on the mark grating and the template grating, and the moire fringe image generates the moire fringe image based on the first diffraction light and the second diffraction light. The application adopts an off-axis illumination system, improves illumination utilization, simplifies the device, reduces the amount of data to be transmitted, and improves production efficiency.

Description

Technical Field

[0001] This invention relates to the field of nanoimprint technology, and more particularly to an off-axis illumination alignment device, a nanoimprint apparatus, and an imprint alignment method. Background Technology

[0002] Nanoimprint lithography is a microfabrication technique that transfers patterns from a template onto a substrate, commonly used in semiconductor manufacturing, photolithography, and other fields. The alignment accuracy during the imprinting process directly affects the final imprint quality.

[0003] Most existing alignment systems use coaxial illumination imaging systems. US Patent US10634995B2 and Chinese Patent CN110088878A both disclose the use of prisms to make the illumination light path and imaging light path coaxial. This system has low illumination light utilization and complex structural design.

[0004] Chinese patent CN111381460B also employs a coaxial illumination imaging system. The illumination light is incident on the wafer marking grating at a Littoral angle, causing its first-order diffracted light to return along the incident light direction. An eight-unit imaging system is used for precise alignment. Chinese patent CN104122746A discloses an imprinting method that obtains the relative position of the target area and the patterned portion of the mold based on the detection results of eight detection units, thereby achieving the alignment requirements during the imprinting process. For example... Figure 1 As shown, the aforementioned existing technologies all require an 8-group imaging system, which is complex, generates a large amount of image data, and has high requirements for data transmission rate, thus affecting production efficiency.

[0005] Therefore, it is imperative to develop a new alignment device to address the current deficiencies and shortcomings. Summary of the Invention

[0006] In view of this, the main objective of the present invention is to provide an off-axis illumination alignment device, a nanoimprint device, and an imprint alignment method, which adopts an off-axis illumination system to improve illumination utilization, simplify the device, reduce the amount of data to be transmitted, and improve production efficiency.

[0007] To achieve the above objectives, as a first aspect of the present invention, an off-axis illumination alignment device is proposed, comprising: an illumination unit providing multiple beams of illumination light, the illumination light illuminating an alignment object in the x and y directions at a certain incident angle; and an imaging unit vertically disposed above the alignment object to acquire a moiré fringe image characterizing the degree of alignment between the alignment object and the template, wherein the illumination light incident on a marker grating on the alignment object and a template grating on the template generates a first diffracted light and a second diffracted light, respectively, and the moiré fringe image is generated based on the first diffracted light and the second diffracted light.

[0008] As a second aspect of the present invention, a nanoimprint apparatus is also provided, comprising: an imprint head for placing a template and moving the template; a motion platform disposed below the imprint head for carrying a wafer to be imprinted; an alignment system including the alignment device described above; and an exposure light source for providing curing light, disposed above the template, wherein the motion platform receives an alignment signal from the alignment system and aligns the wafer with the template based on the alignment signal.

[0009] As a third aspect of the present invention, an imprint alignment method for a nanoimprint apparatus is also proposed. The nanoimprint apparatus described above is used for position alignment. The imprint alignment method includes: adjusting the imprint head and the motion platform so that the wafer marking grating and the template marking grating enter the field of view of the imaging unit; adjusting the imprint head so that the template is pressed down into the depth of focus range of the telecentric lens; the alignment system acquires a moiré fringe image and calculates the positional deviation between the wafer and the template marking grating; and the motion platform moves the wafer and the template for alignment according to the positional deviation.

[0010] Based on the above technical solution, it can be seen that the technical solution of the present invention has at least one of the following beneficial effects compared with the prior art:

[0011] 1. An off-axis lighting system is adopted to improve lighting utilization. The lighting system uses Kohler lighting system to provide uniform lighting.

[0012] 2. The two lighting systems use the same imaging system for imaging. Only four alignment devices are needed for larger wafers, which simplifies the equipment and reduces the amount of data that needs to be transmitted, thereby improving production efficiency.

[0013] 3. By setting the incident angle of the illumination light corresponding to the marking grating, specular reflection light is prevented from entering the imaging system, thus achieving dark-field imaging, ensuring imaging contrast, and improving alignment accuracy.

[0014] It should be understood that the description in the Summary of the Invention is not intended to limit the key or essential features of the embodiments of the present invention, nor is it intended to restrict the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a layout diagram of an existing alignment device;

[0017] Figure 2This is a schematic diagram of the alignment device according to an embodiment of the present invention. Figure 1 ;

[0018] Figure 3 This is a schematic diagram of the alignment device according to an embodiment of the present invention. Figure 2 ;

[0019] Figure 4 This is a schematic diagram of the nanoimprint apparatus according to an embodiment of the present invention;

[0020] Figure 5 This is a top view of a schematic diagram of the nanoimprint apparatus according to an embodiment of the present invention;

[0021] Figure 6 This is a schematic diagram of the marking grating of the wafer and template according to an embodiment of the present invention;

[0022] Figure 7 This is a schematic diagram of moiré fringe image alignment according to an embodiment of the present invention;

[0023] Figure 8 This is a schematic diagram of the dark field imaging principle according to an embodiment of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The terminology used in this invention is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of the invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0026] In the field of nanoimprint lithography, the common alignment method uses a coaxial illumination imaging system. To improve alignment accuracy, alignment of all four corners of the wafer and the template is required. Since most alignment systems utilize the principle of Littoral angle diffraction, the diffracted light returns in different directions depending on the x and y directions of the grating lines marked at a corner. Therefore, two alignment systems are needed for each corner to align the x and y marks separately, requiring a total of eight alignment measurement modules to detect the four corners of the wafer to ensure alignment between the wafer and the template. Figure 1As shown, 7-1 to 7-8 are eight alignment marks set at the four corners of the wafer. 10-1, 20-1, 30-1, 40-1, 50-1, 60-1, 70-1, and 80-1 are alignment measurement modules set at each alignment mark. It can be seen that the component system of this technology is complex, the amount of imaging image data is large, and the response efficiency is low. In order to solve the above problems, this application redesigns the imaging structure, reduces the number of imaging systems by half, and ensures alignment accuracy and improves work efficiency.

[0027] Moiré fringe patterns are optical fringes formed by the superposition of two periodic grating patterns with similar spatial frequencies. They can be generated by various principles such as light-blocking effect, diffraction effect, and interference effect. Two sets of moiré fringe patterns can be used to align two objects (a wafer and a template). Specifically, a light beam passes through two layers of gratings, each layer containing two gratings with similar grating constants, P1 and P2, arranged side-by-side. The correspondence between the two gratings is: P1 corresponds to P2, and P2 corresponds to P1. This process creates a moiré fringe pattern. The moiré fringe pattern has a magnifying effect relative to the gratings, and its phase can be correlated with the relative displacement of the gratings, thus determining the alignment position.

[0028] The first part of this invention proposes an off-axis illumination alignment device 100, such as... Figure 2 As shown, the system includes: an illumination unit 120 providing multiple beams of illumination light, which illuminate the alignment object in the x and y directions at certain incident angles; and an imaging unit 110 vertically positioned above the alignment object to acquire a moiré fringe image characterizing the alignment degree between the alignment object and the template. The illumination light incident on the marker grating on the alignment object and the template grating on the template generates first diffracted light and second diffracted light, respectively, and the moiré fringe image is generated based on the first and second diffracted light. Specifically, it includes one imaging unit 110 and two illumination units 120, wherein the two illumination units 120 are arranged at 90° and emit illumination light respectively.

[0029] Specifically, a coordinate system is constructed based on the working surface of the alignment device 100, such as... Figure 2 and Figure 3As shown, the x-axis, y-axis, and z-axis perpendicular to the horizontal plane of the alignment object are set. One imaging unit 110 and two illumination units 120 are both positioned on the z-axis, at a distance from the horizontal plane of the alignment object. The two illumination units 120 are set at 90°, illuminating the alignment object in the x and y directions respectively. The diffracted light from the two illumination units enters the imaging unit 110 along the z-axis to form a moiré fringe image, which is analyzed and compared for alignment. The alignment objects are a pair of objects A and B positioned vertically. Marker gratings M2 and M1 are respectively set on objects A and B. Alignment of objects A and B is achieved by adjusting the offset of marker gratings M2 and M1. In the alignment process between the wafer and the template, object A is the template and object B is the wafer.

[0030] In a preferred embodiment, the lighting unit 120 includes a light source, a lens, and a reflector arranged sequentially, wherein the angle of incidence of the lighting light is adjusted by setting the angle of the reflector. Specifically, as shown... Figure 3 As shown, the illumination unit 120 is a Kohler illumination system, comprising a light source 121, a first lens 122, a second lens 123, and a reflector 124 arranged sequentially. By adjusting the tilt angle of the reflector 124, the illumination light can be directed onto the marking grating of the alignment object at a specific angle, ensuring that its first-order diffracted light enters the imaging unit 110 while the reflected light cannot enter the imaging unit 110. This achieves image acquisition in a dark field, ensuring high image contrast. Multiple lenses can be provided according to the needs of Kohler illumination.

[0031] In a preferred embodiment, the alignment object is provided with an alignment marker grating. The incident angle is related to the grating period of the alignment object, ensuring that the imaging unit 110 receives the first-order diffracted light from the marker grating to form a dark-field image. The grating period is the grating period of the built-in markers M2 and M1 on the alignment objects A and B. Markers M2 and M1 can be rectangular, cross-shaped, or other specific geometric shapes. Generally, the marking grating lines on a wafer are a checkerboard structure, and the marking grating on a template is a striped grating. During the operation of the alignment device, ensuring that the imaging unit 110 only receives the first-order diffracted light from the marker grating M1 to form a dark-field image helps improve the contrast of the moiré fringe image, thereby improving alignment accuracy. Dark-field imaging can be achieved by simply adjusting the angle of the reflector 124. The device is simple, easy to operate, and also increases the flexibility and adaptability of the equipment.

[0032] In a preferred embodiment, such as Figure 3As shown, the imaging unit 110 includes a telecentric lens 111 and a camera 112, which is a photosensitive sensor camera. To ensure imaging quality, the photosensitive sensor camera can be a CCD (Charge-coupled Device) camera or a CMOS (Complementary Metal-Oxide-Semiconductor) camera.

[0033] In a preferred embodiment, the alignment device 100 further includes a processing unit that receives a moiré fringe image, calculates an offset, and generates an alignment signal to control the movement of the alignment object based on the offset. Specifically, after the camera 112 captures an image, it transmits the moiré fringe image to the processing unit. The processing unit calculates and compares the phase difference between the moiré fringe images, calculates the offset, and then controls the alignment object based on the offset to achieve alignment of alignment object A and alignment object B.

[0034] This invention relates to an alignment device used in semiconductor manufacturing, photolithography, and other fields. It serves as an alignment tool, assists in nanoimprint technology, and improves imprint quality. This device employs off-axis illumination technology and designs the illumination and imaging results to improve the utilization rate of the illumination light. At the same time, it uses a Kohler illumination system to provide uniform illumination light while meeting the conditions for dark-field imaging, ensuring image contrast and improving alignment accuracy.

[0035] The second part of this invention proposes a nanoimprint emulation apparatus 200. In the chip manufacturing process, to achieve the required precision in nanoimprint emulation, an alignment unit is needed to precisely align the wafer and the template. For example... Figure 4 As shown, a three-dimensional Cartesian coordinate system is constructed based on the working surface of the nanoimprinting, including: an imprint head 210 for placing the template 300 and moving the template 300; a motion platform 220 located below the imprint head 210 for supporting the wafer 400 to be imprinted; an alignment system including an alignment device 100 located above the marking grating around the template 300; and an exposure light source 230 providing curing light located above the template 300. The motion platform 220 receives the alignment signal from the alignment system and aligns the wafer 400 with the template 300 based on the alignment signal.

[0036] Due to the requirements of nanoimprint technology and chip precision, it is divided into single-chip imprinting and multi-chip imprinting.

[0037] Specifically, a certain number of rectangular chip areas 410 to be imprinted are generally set on the wafer 400 according to a certain pattern. Different alignment marks are set according to the shape, size, and alignment accuracy requirements of the chip areas. The same number of alignment devices 100 are set according to the number of marks. The chip shape is generally rectangular, requiring a set of alignment marks at each of the four corners of the rectangle, with each alignment mark corresponding to a set of alignment devices 100. For example... Figure 5 As shown, alignment marks are set at the four corners of one of the rectangular chip areas 410, and a set of alignment devices 100 are set around each of the chip 410. The imaging unit 110 is located directly above the alignment marks, and two sets of illumination units 120 are located around the imaging unit 110, respectively, at a 90° angle, illuminating the x and y directions of the alignment marks, so as to achieve precise alignment between the chip 410 and the template 300 above it.

[0038] In the process of multi-chip imprinting, there are alignment marks at the four corners of each chip on the wafer, and each chip needs to be aligned before imprinting.

[0039] In a preferred embodiment, the template 300 is provided with a first template grating along the x-direction and a second template grating along the y-direction; the wafer 400 is provided with a first marking grating along the x-direction and a second marking grating along the y-direction; wherein, the alignment device performs positional alignment of the template and the wafer based on the moiré fringe image formed by the first template grating and the first marking grating or the moiré fringe image formed by the second template grating and the second marking grating.

[0040] Specifically, the wafer uses a checkerboard-patterned grating, and the template uses a striped grating, such as... Figure 6 As shown, the left side shows the first marking grating M1x and the first template grating M2x along the x-direction, and the right side shows the second marking grating M1y and the second template grating M2y along the y-direction, used for alignment in the x and y directions, respectively. The grating periods of the first template grating M2x are P1 and P2, respectively. The grating periods of the first marking grating M1x along the x-direction are reversed compared to those of the first template grating M2x, being P2 and P1, respectively. These two sets of gratings combine to form a moiré fringe image, with a fringe period along the x-direction of PM = P1 * P2 / 2|P1 - P2|. During the alignment process, the imaging unit acquires an image and determines the alignment based on the moiré fringe image within the image, such as... Figure 7 As shown, the top image is an misaligned moiré fringe image, and the bottom image is an aligned moiré fringe image. It is evident that during the alignment process, the image needs to be analyzed, the offset calculated, and the wafer moved until an aligned moiré fringe image is achieved.

[0041] In a preferred embodiment, the motion platform 220 includes a control module and a position movement module. The control module receives an alignment signal, processes it to obtain a movement signal, and sends the movement signal to the position movement module to drive the motion platform, so that the wafer moves to align the chip area to be imprinted with the template.

[0042] Specifically, after the imaging unit 110 acquires the moiré fringe image, it processes the offset, which is the alignment signal, and sends it to the control module of the motion platform. This controls the position movement module to move precisely, driving the motion platform so that the wafer moves along the x or y direction, or even rotates as needed, to align it with the template.

[0043] The nanoimprint apparatus of the present invention uses an off-axis alignment device for alignment operation. The alignment device consists of one imaging unit and two illumination units. Only one alignment device is needed for the same mark, which reduces the number of alignment devices and simplifies the alignment system of the imprint equipment. By utilizing the alignment principle of moiré fringe images, the amount of image data acquired and transmitted is reduced, thereby improving production efficiency and work efficiency.

[0044] The third part of this invention proposes an imprint alignment method for a nanoimprint apparatus, wherein the nanoimprint apparatus described above is used for position alignment, and the steps of the imprint alignment method include:

[0045] S1: Adjust the imprint head and motion platform to bring the wafer marking grating and template marking grating into the field of view of the imaging unit;

[0046] S2: Adjust the impression head so that the template is pressed down into the depth of field range of the telecentric lens;

[0047] S3: The alignment system acquires moiré fringe images and calculates the positional deviation between the wafer and the template marking grating;

[0048] S4: The motion platform moves the wafer to align with the template according to the positional deviation.

[0049] In a preferred embodiment, the present invention further includes a preset step: before the device is started, the angle setting of the mirror in the alignment system needs to be calculated based on the grating period of the marking grating on the wafer to ensure dark field imaging.

[0050] In a preferred embodiment, taking the marking grating in the x-direction as an example, the grating constant of the first marking grating M1x along the y-direction is Pw. Pw directly determines the vertical distance between the alignment system and the template 300, and the setting angle of the reflector inside the illumination unit 120, or in other words, the incident angle of the illumination light from the illumination unit 120. Specifically, as shown... Figure 8As shown, the illumination light, after being deflected by the mirror, illuminates the wafer surface in the yz plane at an incident angle θ = arcsin(λ / Pw). In the zx plane, it can be seen that the ±1st order diffracted light of the incident light, influenced by the marking grating of the template, enters the imaging unit along the z-direction, while the reflected light cannot enter the imaging system. This ensures dark-field imaging and improves image sharpness. The diffraction and interference effects between the marking grating of the wafer and the marking grating of the template in the xz plane form a moiré fringe pattern, which can effectively improve alignment accuracy.

[0051] Based on the above technical solution, it can be seen that the technical solution of the present invention has at least one of the following beneficial effects compared with the prior art:

[0052] 1. An off-axis lighting system is adopted to improve lighting utilization. The lighting system uses Kohler lighting system to provide uniform lighting.

[0053] 2. The two lighting systems use the same imaging system for imaging. Only four alignment devices are needed for larger wafers, which simplifies the equipment and reduces the amount of data that needs to be transmitted, thereby improving production efficiency.

[0054] 3. By setting the incident angle of the illumination light corresponding to the marking grating, specular reflection light is prevented from entering the imaging system, thus achieving dark-field imaging, ensuring imaging contrast, and improving alignment accuracy.

[0055] The foregoing has described specific embodiments of the present invention. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps described in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired results. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An alignment device for off-axis illumination, characterized in that, include: The illumination unit provides multiple beams of illumination light, which illuminate the target in the x and y directions at a certain incident angle. An imaging unit, vertically positioned above the alignment object, acquires a moiré fringe image characterizing the degree of alignment between the alignment object and the template. The illumination light incident on the marking grating on the alignment object and the template grating on the template respectively generates a first diffracted light and a second diffracted light, and the moiré fringe image is generated based on the first and second diffracted light.

2. The alignment device according to claim 1, characterized in that, The lighting unit includes a light source, a lens, and a reflector arranged in sequence, wherein the incident angle of the lighting light is adjusted by setting the angle of the reflector.

3. The alignment device according to claim 1, characterized in that, The alignment object is provided with an alignment marker grating, and the incident angle is related to the grating period of the alignment object.

4. The alignment device according to claim 1, characterized in that, The imaging unit includes a telecentric lens and a camera, wherein the camera is a photosensitive sensor camera.

5. The alignment device according to claim 1, characterized in that, Also includes: The processing unit receives the moiré fringe image, calculates the offset, and generates an alignment signal based on the offset to control the movement of the alignment object.

6. A nanoimprinting device, characterized in that, include: An impression head is used to place the template and move the template. A motion platform, located below the imprint head, is used to support the wafer to be imprinted; An alignment system, comprising the alignment device as described in any one of claims 1-5; An exposure light source, providing curing light, is positioned above the template. The motion platform receives the alignment signal from the alignment system and aligns the wafer with the template based on the alignment signal.

7. The nanoimprint apparatus according to claim 6, characterized in that, The template is provided with a first template grating along the x-direction and a second template grating along the y-direction; the wafer is provided with a first marking grating along the x-direction and a second marking grating along the y-direction; wherein... The alignment device aligns the template with the wafer based on a moiré pattern formed by the first template grating and the first grating and / or a moiré pattern formed by the second template grating and the second marker grating.

8. The nanoimprint apparatus according to claim 6, characterized in that, The motion platform includes a control module and a position movement module, wherein, The control module receives the alignment signal, processes it to obtain a movement signal, and sends the movement signal to the position movement module to drive the motion platform so that the wafer is aligned with the template.

9. An imprint alignment method for a nanoimprint apparatus, characterized in that, Position alignment is performed using the nanoimprint apparatus as described in any one of claims 6-8, wherein the imprint alignment method includes: Adjust the imprint head and motion platform to bring the wafer marking grating and template marking grating into the field of view of the imaging unit; Adjust the impression head so that the template is pressed down into the depth of field range of the telecentric lens; The alignment system acquires moiré fringe images and calculates the positional deviation between the wafer and the template marking grating; The motion platform moves the wafer to align with the template based on the positional deviation.

10. The alignment method according to claim 9, characterized in that, It also includes a preset step: before the device is started, the angle setting of the mirror in the alignment unit needs to be calculated based on the grating period of the marking grating on the wafer to ensure dark field imaging.

Images