Alignment mark structures and methods of forming the same

Abstract

The present disclosure provides an alignment mark structure and a forming method thereof, which comprises: a substrate (1); a mark area (2) comprising an alignment structure (2-2) and a chamfer structure layer (2-1); the alignment structure (2-2) is formed in the substrate (1) as a recessed structure; the chamfer structure layer (2-1) is formed on the surface of the substrate (1) as a convex structure, and the chamfer structure layer (2-1) forms a convex chamfer structure on the edge of the alignment structure (2-2); a non-mark area (6) is arranged around the periphery of the mark area (2), and the upper surface of the non-mark area (6) is lower than the lower surface of the chamfer structure layer (2-1) in the mark area (2). The alignment mark structure of the present disclosure can effectively improve the clarity and contrast of alignment mark detection.

Description

Technical Field

[0001] This disclosure relates to the field of photolithography alignment technology, specifically to an alignment mark structure and a method for forming the same. Background Technology

[0002] In actual IC manufacturing, the entire process, from wafer to final testing and packaging, often involves dozens of steps using a stacking method. Therefore, alignment marks are essential to ensure that the alignment values ​​between the current layer and the preceding layer are within acceptable error ranges. However, the alignment marks are typically affected by previous processes, leading to reduced photolithography alignment accuracy. This is because before a certain photolithography layer, the alignment mark surface may already be covered with thin films such as silicon oxide, silicon nitride, metal layers, or photoresist layers, affecting the clarity and contrast of the alignment marks. Especially with the progressive shrinking of IC manufacturing processes, more layers cover the wafer surface for pattern etching and transfer. These layers will, to some extent, interfere with the alignment signal, causing distortion of the alignment marks and affecting the detection of alignment marks in the preceding photolithography process.

[0003] Figure 1 This is a schematic cross-sectional view of a common alignment mark before the photolithography process, including the alignment mark on the substrate structure and the multilayer thin film covering the surface of the alignment mark. The multilayer thin film has filled in the bottom of the alignment mark, and the surface of the multilayer thin film forms an obtuse angle at the edge of the alignment mark. Because the thickness of the multilayer thin film is uneven at the edge of the alignment mark, alignment light incident on the edge of the alignment mark cannot be reflected perpendicularly in one direction, resulting in unclear alignment signals. Since the bottom of the alignment mark is also largely filled in by the multilayer thin film, the contrast between the bottom of the alignment mark and the substrate surface is greatly reduced.

[0004] Therefore, low contrast of the alignment marks will make it difficult for the CCD camera to detect the alignment mark signal, and unclear edges of the alignment marks will distort the alignment signal detected by the CCD camera, thereby reducing the alignment accuracy and affecting the lithography quality. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the aforementioned issues, this disclosure provides an alignment mark structure and its formation method, which solves the technical problems of unclear alignment signal edges and low contrast during detection by traditional alignment mark structures.

[0007] (II) Technical Solution

[0008] This disclosure provides an alignment marking structure, comprising: a substrate; a marking region including an alignment structure and a chamfer structure layer; the alignment structure is formed in the substrate by etching and is a recessed structure; the chamfer structure layer is formed on the surface of the substrate by deposition and is a protruding structure, wherein the chamfer structure layer forms a protruding chamfer structure at the edge of the alignment structure; and a non-marking region disposed around the periphery of the marking region, wherein the upper surface of the non-marking region is lower than the lower surface of the chamfer structure layer in the marking region.

[0009] Furthermore, a high-reflectivity thin film layer is provided on the bottom and sidewalls of the alignment structure; the thickness of the high-reflectivity thin film layer does not exceed 100 nm, and its material includes one of Au, Al, and Ag.

[0010] Furthermore, the planar dimensions of the alignment structure range from 0.5 to 50 μm, and the recess depth of the alignment structure ranges from 100 to 4000 nm.

[0011] Furthermore, the alignment structure includes one of the following: a cross-shaped alignment mark or a grid-type alignment mark.

[0012] Furthermore, the thickness of the chamfered structure layer does not exceed 100 nm, and the tilt angle of the chamfered structure is 35–55°; the material of the chamfered structure layer is an easily etchable and non-transparent medium, including one of silicon nitride, aluminum nitride, silicon carbide, and polycrystalline silicon.

[0013] Furthermore, the unmarked area is a U-shaped structure, surrounding the alignment structure within a range of 1 to 1000 μm; the unmarked area is formed in the substrate by etching, and its etching depth does not exceed 1 / 2 of the depth of the recessed structure.

[0014] This disclosure also provides a method for preparing the alignment mark structure according to the aforementioned method, comprising: S1, forming a chamfer layer on a substrate; S2, coating a first photosensitive layer; etching a mark area after exposure and development, including sequentially etching the chamfer layer and the substrate to obtain an alignment structure; S3, etching the chamfer layer at the edge of the alignment structure to obtain a raised chamfer structure, and removing the first photosensitive layer; S4, coating a second photosensitive layer; etching the periphery of the mark area after exposure and development, including sequentially etching the chamfer layer and the substrate to obtain a non-marked area and a chamfer structure layer; S5, removing the second photosensitive layer to obtain a target alignment mark structure.

[0015] Furthermore, after S3, there is also S31, which involves depositing a high-reflectivity thin film layer with a thickness not exceeding 100 nm.

[0016] Furthermore, S5 also includes: removing the high-reflectivity thin film layer on the chamfered structure layer.

[0017] Furthermore, the etching method in S3 is dry etching, which includes one of reactive ion etching and inductively coupled plasma etching. The etching gas includes one of SF6, O2, N2, CHF3, Cl2, Ar and C4F8. The tilt angle of the etched raised chamfered structure is 35-55°.

[0018] (III) Beneficial Effects

[0019] The alignment mark structure and its formation method disclosed herein, by setting a higher chamfered structure layer on the marked area and setting a lower unmarked area around the marked area, makes the surface of the marked area closer to the mask and the surface of the unmarked area farther away from the mask. During detection, the contrast of the marked area relative to the unmarked area is greater, and it is easier to obtain the detection signal of the alignment mark. Furthermore, by forming a raised chamfered structure in the chamfered structure layer, it is possible to effectively prevent the deposited multilayer film from accumulating at the edge of the alignment structure, thereby enabling the incident light at the edge of the alignment structure to be reflected in one direction, significantly improving the edge clarity of the alignment structure. Attached Figure Description

[0020] Figure 1 This diagram illustrates the cross-sectional structure of common alignment marks before the photolithography process and a schematic diagram of light reflection.

[0021] Figure 2 The illustration schematically shows the cross-sectional structure of the alignment mark before the photolithography process and a light reflection diagram according to an embodiment of the present disclosure;

[0022] Figure 3 A top view illustrating the positional relationship between marked and unmarked areas according to an embodiment of the present disclosure, and a schematic diagram illustrating their contrast relationship, are shown.

[0023] Figure 4 A flowchart illustrating a method for preparing an alignment mark structure according to an embodiment of the present disclosure is shown schematically;

[0024] Figure 5 This schematically illustrates the processing steps of the alignment mark structure according to an embodiment of the present disclosure;

[0025] Figure 6 The illustration schematically shows an image of an alignment mark with a chamfered structure and a marked area under a CCD camera according to Embodiment 1 of this disclosure;

[0026] Figure 7 The illustration schematically shows an image of the alignment mark without chamfered structure and without a marked area in Comparative Example 1 according to this disclosure, taken under a CCD camera.

[0027] Figure 8 The illustration schematically shows an image of the alignment marks in the unmarked area of ​​Comparative Example 2 according to this disclosure, taken with a CCD camera.

[0028] Figure 9 The image shown schematically illustrates the alignment mark without chamfered structure in Comparative Example 3 according to this disclosure, as seen under a CCD camera.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1. Substrate; 2. Marking area; 3. Multilayer film; 4. Incident light; 5. Reflected light; 5-1. Light reflected from the surface of the multilayer film; 5-2. Light directly reflected from the substrate; 5-3. The sum of irregularly scattered light reflections from the edge of the marking area; 5-4. Light reflected multiple times from inside the multilayer film and back to the air; 2-1. Chamfered structure layer; 2-2. Alignment structure; 6. Unmarked area; 7. Chamfered layer; 8-1. First photosensitive layer; 8-2. Second photosensitive layer; 9-1. First mask; 9-2. Second mask; 10. Exposure light source; 11. High reflectivity film layer. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0033] It should be noted that if the embodiments of this disclosure involve directional indication, the directional indication is only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0034] Embodiments of this disclosure provide an alignment mark structure, see [link to relevant documentation]. Figure 2 It includes: a substrate 1; a marking region 2, including an alignment structure 2-2 and a chamfer structure layer 2-1; the alignment structure 2-2 is formed in the substrate 1 and is a recessed structure; the chamfer structure layer 2-1 is formed on the surface of the substrate 1 and is a protruding structure, and the chamfer structure layer 2-1 forms a protruding chamfer structure at the edge of the alignment structure 2-2; and a non-marking region 6, which is disposed around the periphery of the marking region 2, and the upper surface of the non-marking region 6 is lower than the lower surface of the chamfer structure layer 2-1 in the marking region 2.

[0035] The alignment mark structure disclosed herein includes a mark region 2 formed on a substrate 1 and a non-marker region 6 surrounding the mark region 2. The mark region 2 includes a pre-defined alignment structure 2-2 and a chamfered structure layer 2-1 higher than the initial surface of the substrate 1; the non-marker region 6 is formed in the substrate 1, lower than the lower surface of the chamfered structure layer 2-1 (i.e., the initial surface of the substrate 1), thereby making the mark region 2 higher and the non-marker region 6 lower. In near-contact lithography (such as super-resolution lithography), this allows the surface of the mark region 2 to be closer to the mask, and the non-marker region 6 to have a larger gap relative to the mask. That is, during alignment mark detection, the distance of the non-marker region 6 relative to the mask is greater than the distance of the mark region 2 relative to the mask. This structure makes the non-marker region 6 darker and the mark region 2 brighter under the entire CCD camera, resulting in a greater contrast between the mark region 2 and the non-marker region 6. This makes the alignment structure 2-2 easier to find under the CCD camera, and this structural optimization is especially necessary for near-contact lithography. This solves the problem that the reflected light from the unmarked area 6 is too bright, causing a decrease in the contrast of the alignment structure 2-2 in the marked area 2.

[0036] Furthermore, by forming a raised chamfer structure in the chamfered structure layer 2-1, it is possible to effectively prevent the deposited multilayer thin film 3 from accumulating at the edge of the alignment structure 2-2, such as... Figure 2 As shown, the multilayer film 3 forms a smooth and uniform transition on the chamfered structure, so that the incident light rays illuminating the edge of the alignment structure 2-2 can be reflected in one direction, including the light rays 5-1 reflected from the surface of the multilayer film, the light rays 5-2 directly reflected from the substrate, and the sum of the light rays 5-3 reflected from the irregularly scattered light at the edge of the marking area, thereby significantly improving the edge sharpness of the alignment structure 2-2.

[0037] Based on the above embodiment, a high reflectivity thin film layer 11 is provided on the bottom and sidewalls of the alignment structure 2-2; the thickness of the high reflectivity thin film layer 11 does not exceed 100nm, and its material includes one of Au, Al, and Ag.

[0038] The alignment mark structure disclosed herein may further have a high reflectivity thin film layer 11 disposed on the bottom and sidewalls of the alignment structure 2-2. The high reflectivity thin film layer 11 is made of a material with high reflectivity, including metal thin films such as Au, Al, and Ag. The metal thin film can enhance the intensity of reflected light from the alignment structure 2-2, thereby further improving the contrast of the alignment structure 2-2.

[0039] Based on the above embodiments, the planar dimensions of the alignment structure 2-2 range from 0.5 to 50 μm, and the recess depth of the alignment structure 2-2 ranges from 100 to 4000 nm.

[0040] The alignment structure 2-2 forms an alignment mark pattern on a plane. To facilitate finding the position of the alignment mark pattern, its planar dimension range is usually set within the above range. The etching depth of the alignment structure 2-2 should not be too small, otherwise it will affect the clarity of the alignment structure 2-2 and make it difficult to accurately identify.

[0041] Based on the above embodiments, the alignment structure 2-2 includes one of a cross-shaped alignment mark and a grid-shaped alignment mark.

[0042] The cross-shaped alignment mark is usually used in the rough alignment scenario and has the advantage of quickly finding the relative position relationship between the mask and the wafer; the grid-shaped alignment mark is usually used in the fine alignment scenario and has the advantage of finely adjusting the relative position of each exposure field and the mask template.

[0043] Based on the above embodiments, the thickness of the chamfer structure layer 2-1 does not exceed 100 nm, and the inclination angle of the chamfer structure is 35-55°; the material of the chamfer structure layer 2-1 is a medium that is easy to etch control and non-transparent, including one of silicon nitride, aluminum nitride, silicon carbide, and polysilicon.

[0044] Although the chamfer structure layer 2-1 is used to make the surface of the marking area 2 closer to the mask, its thickness should not exceed 100 nm either, otherwise it will affect the duty cycle of the alignment structure 2-2 observed under the CCD. The inclination angle of the chamfer structure within the above range has the technical effect of uniformly covering the multi-layer film 3. The chamfer structure layer 2-1 is selected as a non-transparent medium to improve the reflectivity of the surface of the marking area 2.

[0045] Based on the above embodiments, the non-marking area 6 is a loop structure and is arranged around the periphery of the alignment structure 2-2 within a range of 1-1000 μm; the non-marking area 6 is formed in the substrate 1 by etching, and its etching depth does not exceed 1 / 2 of the depth of the recessed structure.

[0046] The loop structure is a fully enclosed structure. The non-marking area 6 surrounds and encloses the entire marking area 2, as Figure 3 shown, the marking area 2 and the non-marking area 6 form a complete alignment mark structure. The etching depth of the non-marking area 6 does not exceed 1 / 2 of the depth of the recessed structure. If the etching depth is too deep, it will also affect the contrast between the bottom of the alignment structure 2-2 and the bottom of the non-marking area 6.

[0047] The embodiments of the present disclosure also provide a preparation method of an alignment mark structure according to the foregoing, as Figures 4-5As shown, the process includes: S1, forming a chamfer layer 7 on a substrate 1; S2, coating a first photosensitive layer 8-1; after exposure and development, etching the marking area 2, including sequentially etching the chamfer layer 7 and the substrate 1 to obtain an alignment structure 2-2; S3, etching the chamfer layer 7 at the edge of the alignment structure 2-2 to obtain a raised chamfer structure, and removing the first photosensitive layer 8-1; S4, coating a second photosensitive layer 8-2; after exposure and development, etching the periphery of the marking area 2, including sequentially etching the chamfer layer 7 and the substrate 1 to obtain a non-marking area 6 and a chamfer structure layer 2-1; S5, removing the second photosensitive layer 8-2 to obtain a target alignment marking structure.

[0048] The method for fabricating the alignment mark structure is as follows: After fabricating the chamfer layer 7, the alignment structure 2-2 is first etched, then the raised chamfer structure is etched, and finally the non-marker area 6 is etched to obtain the chamfer structure layer 2-1, thus obtaining the target alignment mark structure. All etching steps involve conventional photolithography processes, and the fabrication method is simple and easy to operate.

[0049] Based on the above embodiment, after S3, it further includes: S31, depositing a high reflectivity thin film layer 11, the thickness of which does not exceed 100nm.

[0050] After etching to obtain the raised chamfered structure and before etching to obtain the unmarked area 6, a high-reflectivity thin film layer 11 can be sputtered and deposited in the alignment structure 2-2 to further improve the contrast of the alignment structure 2-2.

[0051] Based on the above embodiment, S5 further includes: removing the high reflectivity thin film layer 11 on the chamfered structure layer 2-1.

[0052] After depositing the high reflectivity thin film layer 11 in step S31 and removing the second photosensitive layer 8-2, the residual high reflectivity thin film on the upper surface of the chamfered structure layer 2-1 and the upper surface of the unmarked area 6 can also be removed simultaneously, so that the high reflectivity thin film is only formed on the bottom and sidewalls of the alignment structure 2-2.

[0053] Based on the above embodiments, the etching method in S3 is dry etching, which includes one of reactive ion etching and inductively coupled plasma etching. The etching gas includes one of SF6, O2, N2, CHF3, Cl2, Ar and C4F8. The tilt angle of the etched raised chamfer structure is 35 to 55°.

[0054] Dry etching is beneficial for protecting the straightness of the alignment structure. The tilt angle of the chamfer structure can be controlled by etching gas flow rate, etching time, power, cavity pressure, etc.

[0055] The alignment mark structure and its formation method disclosed herein improve the contrast of the alignment structure by, on the one hand, setting a higher chamfered structure layer on the marked area and a lower non-marked area around the marked area, making the surface of the marked area closer to the mask and the surface of the non-marked area farther from the mask; furthermore, by setting a high-reflectivity thin film layer on the bottom and sidewalls of the alignment structure, the intensity of reflected light is enhanced, further improving the contrast of the alignment structure; on the other hand, by forming a raised chamfered structure in the chamfered structure layer, multiple thin films are uniformly covered on the chamfered structure of the marked area, allowing incident light at the edge of the alignment structure to be reflected in one direction, significantly improving the edge sharpness of the alignment structure. Combining these two aspects, this disclosure reduces the distortion of the alignment structure, thereby reducing alignment errors in IC manufacturing.

[0056] The present disclosure will be further described below through specific embodiments. The alignment mark structure and its formation method are specifically described in the following embodiments. However, the following embodiments are merely illustrative of the present disclosure, and the scope of the present disclosure is not limited thereto.

[0057] The alignment mark structure in this embodiment includes a mark region 2 formed on a substrate 1 and a non-marker region 6 surrounding the mark region. The mark region 2 includes a pre-defined alignment structure 2-2 and a chamfered structure layer 2-1. The planar dimensions of the alignment structure 2-2 range from 0.5 to 50 μm. This alignment structure is a recessed structure with an etching depth of 100 to 4000 nm. The chamfered structure layer 2-1 is a protruding structure with a thickness not exceeding 100 nm and a chamfer angle of 35 to 55°. The non-marker region 6 can be a U-shaped region located within a range of 1 to 1000 μm from the edge of the mark region 2. The etching depth of the non-marker region 6 does not exceed half the etching depth of the alignment structure 2-2, and the etching depth of the non-marker region 6 is 100 to 2000 nm.

[0058] The method for preparing the alignment mark structure in this embodiment includes the following steps, such as: Figure 5 As shown:

[0059] Step (1): Prepare substrate 1;

[0060] Step (2): A chamfer layer 7 is prepared on the surface of substrate 1, and the thickness d1 of the chamfer layer 7 is 10-100 nm; equivalent to step S1 above;

[0061] Step (3): Prepare the first photosensitive layer 8-1 on the chamfered layer 7. The thickness d2 of the first photosensitive layer 8-1 is 100~1000nm.

[0062] Step (4): Based on step (3), perform exposure and development. The first mask 9-1 is an alignment mark mask, and the exposure light source 10 is above the first mask 9-1.

[0063] Step (5): Etch the pattern obtained by developing in step (4). First, use the first photosensitive layer 8-1 as a mask to etch the chamfer layer 7, and etch through the chamfer layer 7.

[0064] Step (6): Based on step (5), the first photosensitive layer 8-1 and the chamfered layer 7 are used as the masking etching substrate 1 to obtain the alignment structure 2-2. The etching depth d5 ​​of the alignment structure 2-2 is 100~4000nm; equivalent to step S2 above.

[0065] Step (7): Etch the chamfered structure, with a chamfered structure tilt angle of 35-55°; equivalent to step S3 above;

[0066] Step (8): Remove residual photoresist from the surface of chamfered layer 7;

[0067] Step (9): Selectively prepare a high reflectivity thin film layer 11, the thickness d6 of which is 10-100 nm;

[0068] Step (10): Prepare a second photosensitive layer 8-2 on the chamfered layer 7. The thickness d7 of the second photosensitive layer 8-2 is 100~1000nm.

[0069] Step (11): Expose and develop again based on step (10) to form unmarked area 6;

[0070] Step (12): Based on step (11), etching is performed, and the chamfer layer 7 and the substrate 1 are etched sequentially. The high reflectivity thin film layer 11 can be selectively etched, and the depth d8 of the substrate 1 can be selectively etched to a depth of 10-2000 nm to form the chamfer structure layer 2-1 and the unmarked region 6; equivalent to step S4 above.

[0071] Step (13): Remove the residual photoresist on the surface of substrate 1. Optionally, remove the residual high reflectivity thin film layer on the upper surface of the chamfered structure layer 2-1 and the upper surface of the unmarked area 6 at the same time; equivalent to step S5 above.

[0072] In step (1) above, substrate 1 can be a silicon-based substrate, a sapphire substrate, or a silicon carbide substrate, etc.

[0073] In step (2) above, the material of the chamfer layer 7 should be a medium that is easy to etch and control and is not transparent. It can be one of silicon nitride, aluminum nitride, silicon carbide and polysilicon.

[0074] The first photosensitive layer 8-1 in step (3) and the second photosensitive layer 8-2 in step (10) are both prepared using the same spin coating method.

[0075] In step (4) above, the alignment marks on the alignment mark mask may include cross-shaped alignment marks, grid-type alignment marks, etc.

[0076] The exposure process in steps (4) and (11) above can be close contact exposure, laser direct writing, projection lithography, etc.

[0077] In step (5) above, the etching of the chamfer layer 7 is a dry etching method, including ion beam etching, reactive ion beam etching or inductively coupled plasma etching. The selectable gases are SF6, O2, N2, CHF3, Cl2, Ar and C4F8, etc.

[0078] In step (6) above, the etching of substrate 1 is either dry etching or wet etching, which may include ion beam etching, reactive ion beam etching or inductively coupled plasma etching. The gas can be SF6, CHF3 or Ar. The wet etching solution can be a mixed solution of KOH and IPA, a mixed solution of H2SO4 and H3PO4 in a certain concentration, etc.

[0079] In step (7) above, the tilt angle of the chamfered structure is 35-55°. The etching method for the chamfered structure is dry etching, including reactive ion etching and inductively coupled plasma etching. The selectable gases are SF6, O2, N2, CHF3, Cl2, Ar and C4F8, etc.

[0080] In steps (8) and (13) above, the removal of residual photoresist from the surface etching can be done using either a dry or wet method. Dry removal can be achieved using reactive ion beam etching or inductively coupled plasma etching, with O2 as the etching gas. Wet removal can be achieved using solutions such as ethanol, acetone, or concentrated sulfuric acid.

[0081] In step (9) above, a high-reflectivity thin film is deposited on the bottom and sidewalls of the alignment structure 2-2.

[0082] In step (11) above, the etching of the unmarked region 6 can be either dry etching or wet etching. Dry etching can include ion beam etching, reactive ion beam etching, or inductively coupled plasma etching, and the gas can be SF6, CHF3, or Ar; the solution for wet etching can be a mixed solution of KOH and IPA, a mixed solution of H2SO4 and H3PO4, etc.

[0083] Based on the above scheme, four specific embodiments and three comparative examples are provided below.

[0084] Example 1:

[0085] like Figure 2 As shown, the steps for forming the alignment mark structure in this embodiment are as follows:

[0086] Substrate 1 is a silicon-based material; chamfer layer 7 is made of Si3N4 with a thickness of 20nm and is prepared by magnetron sputtering.

[0087] The first photosensitive layer 8-1 was prepared by spin coating. The material of the first photosensitive layer 8-1 was AR-P3170, and the thickness was 100nm.

[0088] The light-blocking layer on the first mask 9-1 is made of metallic Cr with a thickness of 100 nm and a quartz substrate. The marking pattern on the first mask 9-1 is a grating structure with a period of 20 μm and a length of 40 μm. The area of ​​the marking pattern is 200 μm * 40 μm. The first mask 9-1 also has coarse alignment marks, which are cross-shaped and 10 μm wide. The marking pattern on the first mask 9-1 is exposed to the first photosensitive layer 8-1 using contact lithography.

[0089] After development, the Si3N4 of the chamfer layer 7 was etched using reactive ion beam etching with SF6 and O2 as the etching gases. The gas flow ratio was 5:1, the cavity pressure was 1 Pa, the power was 40 W, the etching time was 20 s, and the etching depth was 20 nm. The alignment structure 2-2 was etched using reactive ion beam etching with SF6 and CHF3 as the etching gases. The cavity pressure was 1 Pa, the power was 100 W, the etching time was 10 min, and the etching depth was 1500 nm. The Si3N4 of the chamfer layer structure 2-1 was etched using reactive ion beam etching with SF6, O2, and N2 as the etching gases. The gas flow ratio of SF6 to O2 was 3:1, the cavity pressure was 1 Pa, the power was 40 W, and the etching time was 10 s, resulting in a chamfer tilt angle of approximately 35°.

[0090] Remove the residual first photosensitive layer 8-1, soak the substrate in acetone until the first photosensitive layer 8-1 falls off, rinse with deionized water and dry the substrate 1;

[0091] A second photosensitive layer 8-2 is prepared by spin-coating AR-1500 photoresist with a thickness of 500 nm. The pattern of the unmarked area 6 on the second mask 9-2 is a square shape, with an inner area of ​​201 μm * 41 μm and an outer area of ​​400 μm * 240 μm. The second mask 9-2 also includes cross-shaped alignment marks that match those on the first mask 9-1. The light-blocking material on the second mask 9-2 is metallic Cr with a thickness of 100 nm, and the substrate is quartz.

[0092] The unmarked area 6 on the second mask 9-2 is exposed to the second photosensitive layer 8-2 using a contact exposure process. After development, the unmarked area 6 is etched with an ion beam for 5 minutes with a substrate rotation angle of 15°. The etching penetrates the chamfer layer 7 and part of the substrate 1 in one pass to form the chamfer structure layer 2-1 and the unmarked area 6. The etching depth of the unmarked area 6 (part of the substrate 1) is 500 nm. The remaining second photosensitive layer 8-2 is removed, and the substrate 1 is soaked in acetone until the second photosensitive layer 8-2 falls off. The substrate 1 is then rinsed with deionized water and dried.

[0093] In this embodiment, the chamfered structure 2-1 covering the alignment structure 2-2 has an angle of about 35°. The thickness of the Si3N4 chamfered structure layer is 20nm. When the multilayer film 3 is covered on the chamfered structure, there is a smooth transition, so that the reflected light is emitted from the same angle, which can improve the clarity of the alignment structure.

[0094] The distance between the unlabeled region 6 and the upper surface of the chamfered structure layer 2-1 is increased to 520 nm, as... Figure 3 As shown, this structure increases the gap between the unmarked area 6 and the mask to a certain extent, reducing the reflectivity of the unmarked area 6 and increasing the contrast of the marked area 2 relative to the unmarked area 6. Figure 6 The image shown is of the alignment mark structure obtained by the method of this embodiment. The image of the structure under the CCD camera is clear, proving that the method of this disclosure is effective.

[0095] Example 2:

[0096] like Figure 2 As shown, the steps for forming the alignment mark structure in this embodiment are as follows:

[0097] Substrate 1 is a silicon-based material; the chamfer layer 7 is made of AlN with a thickness of 100 nm and is prepared by atomic layer deposition.

[0098] The first photosensitive layer 8-1 was prepared by spin coating. The material of the first photosensitive layer 8-1 is AR-P3170, and the thickness is 100nm. The light-blocking layer on the first mask 9-1 is made of metallic Cr, with a thickness of 100nm, and the substrate is quartz. The marking pattern on the first mask 9-1 is a square checkerboard grid with a period of 10μm and an area of ​​400μm*200μm. The first mask 9-1 also has coarse alignment marks, which are cross-shaped and 10μm wide. The marking pattern on the first mask 9-1 was exposed to the first photosensitive layer 8-1 using contact lithography.

[0099] After development, AlN in chamfer layer 7 was etched using reactive ion beam etching with Cl2 and Ar as the etching gases, a gas flow ratio of 5:1, a chamber pressure of 0.5 Pa, a power of 20 W, an etching time of 100 s, and an etching depth of 100 nm. Alignment structure 2-2 was etched using reactive ion beam etching with SF6 and CHF3 as the etching gases, a chamber pressure of 1 Pa, a power of 100 W, an etching time of 25 min, and an etching depth of 4000 nm. AlN in chamfer layer structure 2-1 was etched using reactive ion beam etching with Cl2 and Ar as the etching gases, a gas flow ratio of 3:1, a chamber pressure of 1 Pa, a power of 40 W, and an etching time of 10 s, resulting in a chamfer tilt angle of approximately 40°.

[0100] Remove the residual first photosensitive layer 8-1, soak the substrate in acetone until the first photosensitive layer 8-1 falls off, rinse with deionized water and dry the substrate 1;

[0101] A second photosensitive layer 8-2 is prepared by spin-coating AR-3100 photoresist with a thickness of 1000 nm. The unmarked area 6 on the second mask 9-2 has a U-shaped pattern, with an inner area of ​​401 μm * 201 μm and an outer area of ​​600 μm * 400 μm. The second mask 9-2 also includes cross-shaped alignment marks matching those on the first mask 9-1. The light-blocking material on the second mask 9-2 is metallic Cr with a thickness of 100 nm, and the substrate is quartz. A contact exposure process is used to prepare the second photosensitive layer 8-2. The unmarked area 6 on the second photosensitive layer 8-2 is exposed to the second photosensitive layer 8-2. After development, ion beam etching is used to etch through the chamfer layer 7 and part of the substrate 1 in one go. The etching time is 10 min and the substrate rotation angle is 15° to form the chamfer structure layer 2-1 and the unmarked area 6. The etching depth of the unmarked area 6 (part of the substrate 1) is 1000 nm. The remaining second photosensitive layer 8-2 is removed, and the substrate 1 is soaked in acetone until the second photosensitive layer 8-2 falls off. The substrate 1 is then rinsed with deionized water and dried.

[0102] In this embodiment, the chamfered structure layer 2-1 covering the alignment structure 2-2 has an angle of approximately 40°. The thickness of the AlN chamfered structure layer is 100 nm, providing a smooth transition when the multilayer film 3 covers the chamfered structure, thus allowing reflected light to exit from the same angle and further improving the clarity of the alignment structure. The distance between the unmarked area 6 and the upper surface of the chamfered structure layer 2-1 is increased to 1100 nm. This recessed structure increases the gap between the unmarked area 6 and the mask to a certain extent, reducing the reflectivity of the unmarked area 6 and thus increasing the contrast of the marked area 2 relative to the unmarked area 6.

[0103] Example 3:

[0104] like Figure 2 As shown, the steps for forming the alignment mark structure in this embodiment are as follows:

[0105] Substrate 1 is made of sapphire; chamfer layer 7 is made of SiC with a thickness of 100 nm and is prepared by plasma-enhanced atomic layer deposition.

[0106] The first photosensitive layer 8-1 was prepared by spin coating. The material of the first photosensitive layer 8-1 is AR-P3170, and the thickness is 500nm. The light-blocking layer on the first mask 9-1 is made of metallic Cr, with a thickness of 100nm, and the substrate is quartz. The marking pattern on the first mask 9-1 is a grating structure with a period of 20μm and a length of 40μm. The area of ​​the marking pattern is 200μm*40μm. The first mask 9-1 also has markings for coarse alignment. The markings are cross-shaped and 10μm wide. The marking pattern on the first mask 9-1 is exposed to the first photosensitive layer 8-1 using contact lithography.

[0107] After development, the SiC chamfer layer 7 was etched using inductively coupled plasma etching (ICP-C) with SF6 and C4F8 as the etching gases. The total gas flow rate was 80 sccm, the upper electrode power was 500 W, the lower electrode power was 200 W, the etching time was 2 min, and the etching depth was 100 nm. The alignment structure 2-2 was etched using wet etching with an etching solution volume ratio of V(98% H2SO4):V(85% H3PO4) = 3:1. The etching time was 30 min, and the etching depth was 4000 nm. The SiC chamfer layer structure 2-1 was etched using ICP-C with SF6 and C4F8 as the etching gases. The total gas flow rate was 80 sccm, the upper electrode power was 1000 W, the lower electrode power was 600 W, and the etching time was 30 s, resulting in a chamfer tilt angle of approximately 45°.

[0108] Remove the residual first photosensitive layer 8-1, soak the substrate in acetone until the first photosensitive layer 8-1 falls off, rinse with deionized water and dry the substrate;

[0109] A second photosensitive layer 8-2 is prepared by spin-coating AR-3100 photoresist with a thickness of 1000 nm. The unmarked area 6 on the second mask 9-2 has a U-shaped pattern, with an inner area of ​​201 μm * 41 μm and an outer area of ​​400 μm * 240 μm. The second mask 9-2 also includes cross-shaped alignment marks matching those on the first mask 9-1. The light-blocking material on the second mask 9-2 is metallic Cr with a thickness of 100 nm, and the substrate is quartz. A contact exposure process is used to apply the second photosensitive layer 8-2. The unmarked area 6 on the mask 9-2 is exposed to the second photosensitive layer 8-2; after development, ion beam etching is used to etch through the chamfer layer 7 and part of the substrate 1 in one go. The etching time is 10 min and the substrate rotation angle is 15° to form the chamfer structure layer 2-1 and the unmarked area 6. The etching depth of the unmarked area 6 (part of the substrate 1) is 1000 nm; the residual second photosensitive layer 8-2 is removed, the substrate 1 is soaked in acetone until the second photosensitive layer 8-2 falls off, rinsed with deionized water and the substrate 1 is dried.

[0110] In this embodiment, the chamfered structure layer 2-1 covering the alignment structure 2-2 has an angle of approximately 45°. The thickness of the SiC chamfered structure layer is 100 nm, providing a smooth transition when the multilayer film 3 covers the chamfered structure, thus allowing reflected light to exit from the same angle and further improving the clarity of the alignment structure. The distance between the unmarked area 6 and the upper surface of the chamfered structure layer 2-1 is increased to 1100 nm. This recessed structure increases the gap between the unmarked area 6 and the mask to a certain extent, reducing the reflectivity of the unmarked area 6 and thus increasing the contrast of the marked area 2 relative to the unmarked area 6.

[0111] Example 4:

[0112] like Figure 2 As shown, the steps for forming the alignment mark structure in this embodiment are as follows:

[0113] Substrate 1 is a silicon-based material; chamfer layer 7 is made of Si3N4 with a thickness of 20nm and is prepared by magnetron sputtering.

[0114] The first photosensitive layer 8-1 was prepared by spin coating. The material of the first photosensitive layer 8-1 was AR-P3170, and the thickness was 100 nm. The light-blocking layer on the first mask 9-1 was made of metallic Cr, with a thickness of 100 nm, and the substrate was quartz. The marking pattern on the first mask 9-1 was a grating with a period of 20 μm and a length of 40 μm. The area of ​​the marking pattern was 200 μm * 40 μm. The first mask 9-1 also had markings for coarse alignment. The markings were cross-shaped and 10 μm wide. The marking pattern on the first mask 9-1 was exposed to the first photosensitive layer 8-1 using contact lithography.

[0115] After development, the Si3N4 of the chamfer layer 7 was etched using reactive ion beam etching. The etching gases were SF6 and O2, with a gas flow rate ratio of 5:1, a cavity pressure of 1 Pa, a power of 40 W, an etching time of 20 s, and an etching depth of 20 nm. The alignment structure 2-2 was etched using reactive ion beam etching. The etching gases were SF6 and CHF3, with a cavity pressure of 1 Pa, a power of 100 W, an etching time of 10 min, and an etching depth of 1500 nm. The Si3N4 of the chamfer layer 7 was etched using reactive ion beam etching. The etching gases were SF6, O2, and N2, with a gas flow rate ratio of SF6 to O2 of 3:1, a cavity pressure of 1 Pa, a power of 20 W, and an etching time of 15 s, resulting in a tilt angle of approximately 55° for the chamfer structure layer 2-1.

[0116] Remove the residual first photosensitive layer 8-1, soak the substrate 1 in acetone until the first photosensitive layer 8-1 falls off, rinse with deionized water and dry the substrate 1.

[0117] A high-reflectivity thin film layer 11 was prepared by magnetron sputtering to deposit an Ag layer on the surface of substrate 1. The thickness of the Ag layer was 10 nm.

[0118] A second photosensitive layer 8-2 is prepared by spin-coating AR-1500 photoresist with a thickness of 500 nm. The unmarked area 6 on the second mask 9-2 has a U-shaped structure with an inner area of ​​201 μm * 41 μm and an outer area of ​​400 μm * 240 μm. The second mask 9-2 also includes cross-shaped alignment marks matching those on the first mask 9-1. The light-blocking material on the second mask 9-2 is metallic Cr with a thickness of 100 nm, and the substrate is quartz. A contact exposure process is used to expose the unmarked area 6 on the second mask 9-2 onto the second photosensitive layer. 8-2; After development, etch the unmarked area 6 using ion beam etching for 5 minutes with a substrate rotation angle of 15°; The chamfer layer 7 and high reflectivity thin film layer 11 on the unmarked area 6 are etched clean in one go using this method, and then the unmarked area 6 on the substrate 1 is etched. The etching depth of the unmarked area 6 (part of the substrate 1) is 500 nm; Remove the residual second photosensitive layer 8-2, soak the substrate in acetone until the second photosensitive layer 8-2 falls off, remove the residual high reflectivity thin film layer 11 on the alignment structure 2-2, rinse with deionized water and dry the substrate.

[0119] In this embodiment, in addition to the chamfered structure layer 2-1 and the unmarked area 6, a high reflectivity film 11 is added. The high reflectivity film layer 11 is added to the bottom and sidewalls of the alignment structure 2-2, which can further improve the contrast of the alignment structure 2-2.

[0120] Comparative Example 1:

[0121] The substrate 1 of the alignment mark structure in this comparative example is made of silicon. The first photosensitive layer 8-1 is prepared by spin coating. The material of the first photosensitive layer 8-1 is AR-P3170, and its thickness is 100 nm. The light-blocking layer on the first mask 9-1 is made of metallic Cr, with a thickness of 100 nm, and the substrate is quartz. The marking pattern on the first mask 9-1 is a grating with a period of 20 μm and a length of 40 μm. The area of ​​the marking pattern is 200 μm * 40 μm. m; The marking pattern on the first mask 9-1 is exposed to the first photosensitive layer 8-1 using contact lithography; After development, the alignment structure 2-2 is etched using reactive ion beam etching with SF6 and CHF3 as etching gases, a cavity pressure of 1 Pa, a power of 100 W, an etching time of 10 min, and an etching depth of 1500 nm; The residual first photosensitive layer 8-1 is removed, the substrate is soaked in acetone until the residual adhesive of the first photosensitive layer 8-1 is removed, the substrate is rinsed with deionized water and dried.

[0122] The comparative example prepared as follows: Figure 1 As shown in the alignment mark structure, after a multilayer thin film 3 is prepared on the substrate with the alignment mark, the alignment light incident on the edge of the alignment structure 2-2 is not clear because the thickness of the multilayer thin film is uneven at the edge of the alignment structure 2-2. The light reflected from the surface of the multilayer thin film 5-1, the light directly reflected from the substrate 5-2, the sum of the light reflected from the irregularly scattered light at the edge of the mark area 5-3, and the light reflected back to the air after multiple reflections inside the multilayer thin film 5-4 cannot be reflected perpendicularly in one direction.

[0123] like Figure 7 As shown, it can be seen that the marked areas without non-marked areas as recessed structures in this comparative example have low contrast under the CCD camera, and the alignment marks cannot be seen clearly; at the same time, due to the lack of a chamfered structure layer, the edge clarity of the grating marks is very low, and the edge of the grating marks cannot be identified, thus making it impossible to carry out subsequent alignment work.

[0124] Comparative Example 2:

[0125] The steps for forming the alignment mark structure in this comparative example are as follows:

[0126] Substrate 1 is a silicon-based material; chamfer layer 7 is made of Si3N4 with a thickness of 20nm and is prepared by magnetron sputtering.

[0127] The first photosensitive layer 8-1 was prepared by spin coating. The material of the first photosensitive layer 8-1 was AR-P3170, and the thickness was 100 nm. The light-blocking layer on the first mask 9-1 was made of metallic Cr, with a thickness of 100 nm, and the substrate was quartz. The marking pattern on the first mask 9-1 was a grating with a period of 20 μm and a length of 40 μm. The area of ​​the marking pattern was 200 μm * 40 μm. The marking pattern on the first mask 9-1 was exposed to the first photosensitive layer 8-1 using contact lithography.

[0128] After development, the Si3N4 of the chamfer layer 7 was etched using reactive ion beam etching with SF6 and O2 as the etching gases. The gas flow ratio was 5:1, the cavity pressure was 1 Pa, the power was 40 W, the etching time was 20 s, and the etching depth was 20 nm. The alignment structure 2-2 was etched using reactive ion beam etching with SF6 and CHF3 as the etching gases. The cavity pressure was 1 Pa, the power was 100 W, the etching time was 10 min, and the etching depth was 1500 nm. The chamfer layer 7 was etched using reactive ion beam etching with SF6, O2, and N2 as the etching gases. The gas flow ratio of SF6 to O2 was 3:1, the cavity pressure was 1 Pa, the power was 20 W, and the etching time was 15 s, so that the tilt angle of the chamfer structure layer 2-1 was approximately 55°. The residual first photosensitive layer 8-1 was removed, and the substrate 1 was soaked in acetone until the first photosensitive layer 8-1 was detached. The substrate 1 was then rinsed with deionized water and dried.

[0129] The alignment mark structure prepared in this comparative example contains a chamfered structural layer but lacks non-marker regions. For example... Figure 8 As shown, it can be seen that the marked areas without non-marked areas as recessed structures have low contrast under CCD cameras, making the alignment marks unclear and thus affecting subsequent alignment work.

[0130] Comparative Example 3:

[0131] The steps for forming the alignment mark structure in this comparative example are as follows:

[0132] Substrate 1 is a silicon-based material; the first photosensitive layer 8-1 is prepared by spin coating. The material of the first photosensitive layer 8-1 is AR-P3170 and the thickness is 100nm.

[0133] The light-blocking layer on the first mask 9-1 is made of metallic Cr with a thickness of 100 nm, and the substrate is quartz. The marking pattern on the first mask 9-1 is a grating with a period of 20 μm and a length of 40 μm. The area of ​​the marking pattern is 200 μm * 40 μm. The first mask 9-1 also has markings for coarse alignment, which are cross-shaped and 10 μm wide. The marking pattern on the first mask 9-1 is exposed to the first photosensitive layer 8-1 using contact lithography. The alignment structure 2-2 is etched using reactive ion beam etching with SF6 and CHF3 as the etching gases, a cavity pressure of 1 Pa, a power of 100 W, an etching time of 10 min, and an etching depth of 1500 nm.

[0134] Remove the residual first photosensitive layer 8-1, soak the substrate 1 in acetone until the first photosensitive layer 8-1 is detached, rinse with deionized water and dry the substrate 1; prepare the second photosensitive layer 8-2, spin-coate the photoresist AR-P3170 with a thickness of 100nm; the unmarked area 6 on the second mask 9-2 has a U-shaped structure, with an inner circle area of ​​201μm*41μm and an outer circle area of ​​400μm*240μm; the second mask 9-2 also includes cross-shaped alignment marks that match the first mask 9-1 for coarse alignment; the light-blocking material on the second mask 9-2 is metallic Cr with a thickness of 100nm, and the substrate is quartz;

[0135] The unmarked area 6 on the second mask 9-2 is exposed to the second photosensitive layer 8-2 using a contact exposure process. After development, the unmarked area 6 is etched using reactive ion beam etching with SF6 and CHF3 as the etching gases, a cavity pressure of 1 Pa, a power of 50 W, an etching time of 3 min, and an etching depth of 500 nm. The residual second photosensitive layer 8-2 is removed, and the substrate 1 is soaked in acetone until the second photosensitive layer 8-2 is detached. The substrate 1 is then rinsed with deionized water and dried.

[0136] The alignment mark structure prepared in this comparative example does not include a chamfered structure layer, but only contains the non-marked area. After fabricating a multilayer thin film 3 on the substrate of this alignment mark structure, the light illuminating the alignment signal, which is reflected multiple times within the multilayer thin film and then back into the air, cannot be reflected perpendicularly in one direction, resulting in an unclear alignment signal. Figure 9 As shown, it can be seen that the edge of the alignment mark structure grating without the chamfered structure layer has very low clarity, making it impossible to identify the edge of the grating mark and thus impossible to perform subsequent alignment work.

[0137] This disclosure optimizes the structure and layout of alignment marks, enabling the alignment marks to have clear edges and contrast under the alignment detection system, thereby improving the detection capability of alignment signals, reducing the distortion of alignment signals, and achieving the goal of reducing overlay errors in IC manufacturing.

[0138] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. An alignment mark structure, characterized in that, include: Substrate (1); The marking area (2) includes an alignment structure (2-2) and a chamfer structure layer (2-1); the alignment structure (2-2) is formed in the substrate (1) and is a recessed structure; the chamfer structure layer (2-1) is formed on the surface of the substrate (1) and is a protruding structure, and the chamfer structure layer (2-1) forms a protruding chamfer structure at the edge of the alignment structure (2-2); The unmarked area (6) is disposed around the periphery of the marked area (2), and the upper surface of the unmarked area (6) is lower than the lower surface of the chamfered structure layer (2-1) in the marked area (2); the unmarked area (6) is formed in the substrate (1) by etching, and its etching depth does not exceed 1 / 2 of the depth of the recessed structure.

2. The alignment mark structure according to claim 1, characterized in that, The bottom and sidewalls of the alignment structure (2-2) are provided with a high reflectivity thin film layer (11). The thickness of the high reflectivity thin film layer (11) is no more than 100 nm, and its material includes one of Au, Al and Ag.

3. The alignment mark structure according to claim 1, characterized in that, The planar dimensions of the alignment structure (2-2) range from 0.5 to 50 μm, and the recess depth of the alignment structure (2-2) ranges from 100 to 4000 nm.

4. The alignment mark structure according to claim 3, characterized in that, The alignment structure (2-2) includes one of a cross-shaped alignment mark and a grid-type alignment mark.

5. The alignment mark structure according to claim 1, characterized in that, The thickness of the chamfered structure layer (2-1) does not exceed 100 nm, and the tilt angle of the chamfered structure is 35~55°; The material of the chamfered structure layer (2-1) is a non-transparent medium that is easy to etch and control, including one of silicon nitride, aluminum nitride, silicon carbide, and polycrystalline silicon.

6. The alignment mark structure according to claim 3, characterized in that, The unmarked area (6) is a U-shaped structure, surrounding the alignment structure (2-2) within a range of 1~1000 μm.

7. A method for preparing an alignment mark structure according to any one of claims 1 to 6, characterized in that, include: S1, a chamfer layer (7) is formed on the substrate (1); S2, coat the first photosensitive layer (8-1); after exposure and development, etch the marking area (2), including sequentially etching the chamfer layer (7) and the substrate (1) to obtain the alignment structure (2-2). S3, the chamfer layer (7) is etched at the edge of the alignment structure (2-2) to obtain a raised chamfer structure, and the first photosensitive layer (8-1) is removed. S4, coat the second photosensitive layer (8-2); after exposure and development, etch the periphery of the marked area (2), including etching the chamfer layer (7) and the substrate (1) in sequence to obtain the unmarked area (6) and the chamfer structure layer (2-1); the etching depth of the unmarked area (6) does not exceed 1 / 2 of the depth of the recessed structure; S5, remove the second photosensitive layer (8-2) to obtain the target alignment mark structure.

8. The method for preparing the alignment mark structure according to claim 7, characterized in that, Following S3, the following also includes: S31, deposit a high reflectivity thin film layer (11) with a thickness not exceeding 100 nm.

9. The method for preparing the alignment mark structure according to claim 8, characterized in that, The S5 also includes: Remove the high-reflectivity thin film layer (11) on the chamfered structure layer (2-1).

10. The method for preparing the alignment mark structure according to claim 7, characterized in that, The etching method in S3 is dry etching, which includes one of reactive ion etching and inductively coupled plasma etching. The etching gas includes one of SF6, O2, N2, CHF3, Cl2, Ar and C4F8. The angle of inclination of the chamfered structure obtained by etching is 35~55°.

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