Preparation method of wafer surface register mark and metal register mark
By preparing metal plate marks on the wafer surface, the problem of plate marks being easily destroyed in the subsequent process is solved, and the intercalation accuracy and identification accuracy of plate marks are improved.
Patent Information
- Application Number
- CN202411954753.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-27
- Publication Date
- 2025-03-11
AI Technical Summary
In the prior art, the wafer surface typing marking is easily corroded and damaged in subsequent process steps, resulting in incompleteness, thereby reducing the incision accuracy and increasing position error.
Through the optimization of the preparation process, metal plate marks are prepared on the wafer surface, and metal stripping process is used to form plate marks of metal materials to avoid them being destroyed in subsequent processes.
The metallic plate logo is more durable and is not easily damaged by chemical and physical processes, ensuring its integrity, improving the intercalation accuracy, reducing position errors, and increasing the recognition accuracy of plate logos due to the good reflective characteristics.
Smart Images
Figure CN119596648A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of semiconductor processing, and specifically provides a method for preparing a wafer surface alignment mark and a metal alignment mark. Background Art
[0002] The photolithography machine is a key device for manufacturing microelectronic devices and plays a vital role in the chip manufacturing process. The overlay accuracy of the photolithography machine refers to the pattern alignment accuracy that can be achieved when manufacturing chips.
[0003] The photolithography process usually includes the following steps: projecting a pattern on a mask onto a photosensitive material and forming the pattern through a series of chemical and physical processes. The overlay accuracy determines the accuracy and quality of the final pattern.
[0004] The registration mark plays a vital role in the photolithography process and is one of the important factors to ensure the accuracy of the overlay. The registration mark is a specific pattern engraved on the wafer, which is used to align the pattern of each layer during the photolithography process of different layers. These marks help the photolithography machine to accurately position so that the multi-layer patterns can be accurately superimposed.
[0005] In the semiconductor laser manufacturing process, multiple overlays are often required. To avoid the accumulation of multi-layer overlay errors, the alignment marks needed for subsequent multi-layer overlays are usually formed on the wafer after the first photolithography and etching. The subsequent photolithography process is based on the existing marks on the wafer to perform layer-by-layer overlay.
[0006] However, the sidewall edges of the alignment marks made by existing processes will be gradually damaged as subsequent process steps (such as wet etching) proceed, and this damage will have a negative impact on the overlay accuracy. The alignment marks play a role in positioning and alignment during the photolithography process to ensure that the patterns at all levels are correctly superimposed. Incomplete alignment marks may lead to difficulties in positioning and alignment, reduce overlay accuracy, and increase position errors. At the same time, according to process requirements and substrate characteristics, the etching depth in some steps is very shallow, and some substrates have good light transmittance. When preparing transparent alignment marks, it is difficult to distinguish the alignment marks in subsequent overlay steps. Summary of the invention
[0007] In order to solve the above problems, the present invention provides a method for preparing a wafer surface alignment mark and a metal alignment mark, by optimizing the preparation process, a metal alignment mark is prepared on the wafer surface by a metal stripping process, so as to avoid the alignment mark being corroded and damaged in the subsequent process, resulting in an incomplete alignment mark, thereby reducing the overlay accuracy. At the same time, since the metal alignment mark has good reflective properties in the photolithography step, it can provide better boundary properties and contrast, which is conducive to human eye recognition and machine recognition, and can increase the accuracy of subsequent alignment, avoiding the problem of reduced overlay accuracy caused by damage to the alignment mark or low contrast.
[0008] To achieve the above object, the technical solution created by the present invention is implemented as follows: The method for preparing a wafer surface alignment mark provided by the present invention comprises: providing a wafer; forming a strippable mask with a registration mark pattern on the wafer; growing a layer of metal on the surface of the wafer and the strippable mask; The strippable mask and the metal grown on the upper surface of the strippable mask are stripped off to form a metal plate alignment mark.
[0009] Preferably, the preparation process of the strippable mask is as follows: Spin coating a positive photoresist on the wafer; A mask having a light-transmitting area identical to the alignment mark pattern to be prepared is provided, and the positive photoresist is exposed and developed using the mask. The positive photoresist at a position on the wafer corresponding to the light-transmitting area of the mask is retained to obtain the strippable mask.
[0010] Preferably, the spin coating thickness of the positive photoresist is 1 μm-3 μm.
[0011] Preferably, the preparation process of the strippable mask is as follows: Spin coating a negative photoresist on the wafer; A mask having a shading area identical to the alignment mark pattern to be prepared is provided, and the negative photoresist is exposed and developed using the mask. The negative photoresist at a position on the wafer corresponding to the shading area of the mask is retained to obtain the strippable mask.
[0012] Preferably, the spin coating thickness of the negative photoresist is 1 μm-3 μm.
[0013] Preferably, the thickness of the grown metal is 100nm-500nm.
[0014] Preferably, the grown metal is one of chromium, aluminum, chromium, aluminum, titanium, platinum and gold.
[0015] A metal alignment mark is prepared by using a method for preparing an alignment mark on a wafer surface.
[0016] Compared with the prior art, the invention can achieve the following beneficial effects: The present invention proposes for the first time to prepare a metal alignment mark on the surface of a wafer, and provides a complete preparation process. The metal alignment mark is prepared by a metal stripping process using photoresist. The alignment mark is protected by metal, making the alignment mark more durable and not easily damaged by chemical and physical processes, thereby ensuring its integrity in subsequent processes, avoiding damage to the sidewall edge of the alignment mark in subsequent processes, thereby reducing the accuracy of the alignment mark, making it difficult to use the alignment mark for positioning and alignment during the manufacturing process of a semiconductor laser, reducing the overlay accuracy, and multiple overlays will also cause error accumulation. At the same time, according to process requirements and substrate characteristics, some steps have a very shallow etching depth, and some substrates have good light transmittance, making it difficult to distinguish the alignment mark in subsequent overlay steps. The metal alignment mark has better reflective properties than the transparent alignment mark, and can provide better boundary characteristics and contrast, which is conducive to human eye recognition and machine recognition, and can increase the accuracy of subsequent alignment, avoiding the problem of reduced overlay accuracy caused by damage to the alignment mark or low contrast. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings: Figure 1 is a flow chart of preparing wafer surface alignment marks according to an embodiment of the present invention; Figure 2 is a schematic diagram of a first mask provided according to an embodiment of the present invention; Figure 3 is a schematic diagram of a second mask provided according to an embodiment of the present invention; Figure 4 Schematic diagram of a strippable mask prepared by a second mask plate according to an embodiment of the present invention. DETAILED DESCRIPTION
[0018] In order to make the purpose, technical scheme and advantages of the invention clearer, the invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the invention and do not constitute a limitation to the invention. Similar components in different embodiments use associated similar component numbers. In the following embodiments, many detailed descriptions are to enable the invention to be better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other components, materials, and methods. In some cases, some operations related to the invention are not shown or described in the specification, in order to avoid the core part of the invention being overwhelmed by too much description, and for those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.
[0019] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to form various implementation methods. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of clearly describing a certain embodiment and are not meant to be a necessary sequence, unless otherwise specified that a certain sequence must be followed.
[0020] In the description of the invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the invention, unless otherwise specified, the meaning of "multiple" is two or more.
[0021] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.
[0022] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.
[0023] See also Figure 1 In one embodiment of the present invention, a method for preparing a wafer surface alignment mark is provided. As the existing alignment mark is carried out in subsequent process steps (such as wet etching), its side wall edge will be gradually destroyed, which will lead to reduced positioning and alignment accuracy of the alignment mark during the photolithography process, and it is impossible to ensure that the patterns of each layer are correctly superimposed. Therefore, in order to solve the above problems, the embodiment of the present invention forms a metal alignment mark by improving the process steps, protects the integrity of the alignment mark, and thus improves the overlay accuracy. The specific preparation process of the metal alignment mark is as follows: S1: Provide a wafer that needs to be prepared with a plate mark, and use a coating machine to evenly spin-coat photoresist on the surface of the wafer to form a layer of photoresist film, the thickness of which is between 1 micron and 3 microns. Expose and develop the photoresist film through a mask to prepare a strippable mask with a plate mark pattern.
[0024] The photoresist may be either positive photoresist or negative photoresist. Specifically, When a negative photoresist is used, due to the photosensitive property of the negative photoresist, a photocuring reaction will be triggered after exposure, causing a significant change in the physical properties of the exposed area, especially the solubility and affinity. This change causes the unexposed area of the negative photoresist to dissolve in the developer, while the exposed area does not dissolve in the developer. During the development process, the unexposed part can be removed by the developer, while the photoresist area that hardens after exposure is retained to prepare a strippable mask. Therefore, when a negative photoresist is used in this step, the corresponding mask plate should use a mask plate whose light-shielding area pattern is the same as the alignment mark pattern to be prepared, and whose light-transmitting area pattern is mutually interlocked with the alignment mark pattern to be prepared.
[0025] Please refer to Figure 2 After the wafer surface is spin-coated with negative photoresist, Figure 2The mask shown is used to expose a negative photoresist film, which is then developed. The negative photoresist on the unexposed area is dissolved and removed by the developer, while the negative photoresist on the exposed area is solidified and retained. Therefore, after development, a negative photoresist pattern having the same pattern as the light-transmitting area of the mask is formed on the wafer surface. The negative photoresist pattern serves as a strippable mask.
[0026] Figure 2 The light-transmitting area of the strippable mask prepared in the process (i.e., the exposed area on the wafer surface) is in the shape of a "cross" on the upper row and a "field" on the lower row that fits in with the upper row. When the alignment mark to be prepared is in the shape of a "field" on the upper row and a "cross" on the lower row that fits in with the upper row, the following method can be used: Figure 3 Another mask shown in FIG. 1 is used as an example of a mask having only one column. The mask can be used to prepare the following Figure 4 The strippable mask is shown.
[0027] As a feasible embodiment, when positive photoresist is used, due to the photosensitivity of positive photoresist, the exposed area will undergo a chemical reaction, soften and dissolve in the developer, while the unexposed photoresist will remain on the wafer to form a pattern identical to the shading area. Therefore, when positive photoresist is used in this step, the corresponding mask should use a mask whose pattern in the light-transmitting area is the same as the alignment mark pattern to be prepared, and whose pattern in the light-shading area is mutually interlocked with the alignment mark pattern to be prepared.
[0028] After the positive photoresist is spin-coated on the wafer surface, the above-mentioned mask needs to be exposed and developed after exposure. The positive photoresist on the exposed area is dissolved and removed by the developer, while the positive photoresist on the unexposed area is retained. Therefore, after development, a positive photoresist pattern with the same pattern as the shading area of the mask will be formed on the wafer surface, and the positive photoresist pattern can be used as a strippable mask later.
[0029] S2: After a strippable mask is formed on the surface of the wafer, a layer of metal is grown on the surface of the wafer by magnetron sputtering equipment or other electron beam evaporation equipment. The metal layer can usually be one of chromium (Cr), aluminum (Al), titanium (Ti), platinum (Pt), and gold (Au). The thickness of the metal growth is 100nm-500nm. It can be understood that the metal growth in this process includes both areas not covered by the strippable mask and areas covered by the strippable mask. In the areas not covered by the strippable mask, the metal grows directly on the surface of the wafer; while in the areas covered by the strippable mask, the metal grows on the strippable mask and indirectly grows on the surface of the wafer through the strippable mask.
[0030] S3: Since the metal grown on the area covered by the strippable mask is indirectly grown on the wafer surface through the second mask, in order to remove the metal in the non-alignment mark area, the wafer after the metal is grown in S2 needs to be immersed in the photoresist stripping solution to completely dissolve the strippable mask. Therefore, the metal grown on the strippable mask will also be stripped off, while the area not covered by the strippable mask, where the metal is directly grown on the wafer surface, will be retained to form a metal alignment mark, which is used for overlay in subsequent processes.
[0031] As a preferred embodiment, the strippable mask may also be removed by ultrasonic mechanical removal.
[0032] The present invention is designed for the first time to solve the problem that the traditional plate registration mark etching depth is shallow, the transparent plate registration mark is difficult to see clearly, and it is easy to be damaged in the subsequent process. By optimizing the process steps, a metal plate registration mark is designed and prepared, and the present invention combines the etching process with the metal stripping process to ensure the preparation accuracy of the plate registration mark. Compared with the process of direct growth or metal coating, it has higher accuracy and practical value. The pattern of the metal plate registration mark shown in the embodiment of the present invention is only an example, and its specific pattern can also be replaced by other patterns, and masks with different patterns are used accordingly to form strippable masks with different patterns. In addition, multiple overlays can also be performed.
[0033] In short, the above description is only a preferred embodiment of this specification and is not intended to limit the protection scope of this specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this specification shall be included in the protection scope of this specification.
[0034] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.
[0035] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.
[0036] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.
Claims
1. A method for preparing a wafer surface alignment mark, characterized in that: include: providing a wafer; forming a strippable mask with a registration mark pattern on the wafer; growing a layer of metal on the surface of the wafer and the strippable mask; The strippable mask and the metal grown on the upper surface of the strippable mask are stripped off to form a metal plate alignment mark.
2. The method for preparing a wafer surface alignment mark according to claim 1, characterized in that: The preparation process of the strippable mask is as follows: Spin coating a positive photoresist on the wafer; A mask having a light-transmitting area identical to the alignment mark pattern to be prepared is provided, and the positive photoresist is exposed and developed using the mask. The positive photoresist at a position on the wafer corresponding to the light-transmitting area of the mask is retained to obtain the strippable mask.
3. The method for preparing a wafer surface alignment mark according to claim 2, characterized in that: The spin coating thickness of the positive photoresist is 1 μm-3 μm.
4. The method for preparing a wafer surface alignment mark according to claim 1, characterized in that: The preparation process of the strippable mask is as follows: Spin coating a negative photoresist on the wafer; A mask having a shading area identical to the alignment mark pattern to be prepared is provided, and the negative photoresist is exposed and developed using the mask. The negative photoresist at a position on the wafer corresponding to the shading area of the mask is retained to obtain the strippable mask.
5. The method for preparing a wafer surface alignment mark according to claim 4, characterized in that: The spin coating thickness of the negative photoresist is 1 μm-3 μm.
6. The method for preparing a wafer surface alignment mark according to claim 1, characterized in that: The thickness of the grown metal is 100nm-500nm.
7. The method for preparing a wafer surface alignment mark according to claim 1, characterized in that: The grown metal is one of chromium, aluminum, chromium, aluminum, titanium, platinum, and gold.
8. A metal registration mark, characterized in that: The wafer surface alignment mark is prepared by the method for preparing the wafer surface alignment mark as described in any one of claims 1 to 7.