Ion implantation method for semiconductor structures
By employing a process sequence of two exposures and one development, the problems of photoresist residue and pattern deformation at the bottom of deep trenches were solved, enabling precise ion implantation of semiconductor devices and improving device performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SIEN (QINGDAO) INTEGRATED CIRCUITS CO LTD
- Filing Date
- 2026-05-18
- Publication Date
- 2026-06-26
Smart Images
Figure CN122294844A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of semiconductor technology, and more particularly to an ion implantation method for a semiconductor structure. Background Technology
[0002] In some semiconductor device fabrication processes, ion implantation is required at the bottom of deep trenches. For example, in insulated gate bipolar transistor (IGBT) devices, P-type doping at the bottom of a portion of the deep trench (TH) structure can optimize the electric field distribution at the bottom of the trench during reverse breakdown, thereby improving device performance.
[0003] Current processes typically use positive photoresist as a mask, forming an implantation window in the desired area through exposure and development, thus achieving ion implantation. However, the exposure light often fails to reach the bottom of the trench sufficiently to react with the photoresist, resulting in photoresist residue at the bottom of the trench after development, preventing the formation of an effective implantation window. To improve the photosensitivity problem in deep trenches, existing technologies have attempted to use negative photoresist. However, during development, the developer tends to laterally erode the photoresist at the bottom of the deep trench, causing photoresist detachment or mask pattern deformation, again hindering precise ion implantation.
[0004] This shows that it is difficult to achieve precise ion implantation at the bottom of the deep trenches in semiconductor devices. Summary of the Invention
[0005] This application provides an ion implantation method for semiconductor structures to solve the problem that ion implantation is difficult to achieve at the bottom of deep trenches in semiconductor devices.
[0006] This application provides a semiconductor structure ion implantation method, including:
[0007] A substrate is provided having deep trenches;
[0008] A first positive photoresist layer is formed on the surface of the substrate;
[0009] A first exposure is performed, wherein a first exposure dose is used to expose the first positive photoresist layer at the bottom of the deep trench to light;
[0010] A second positive photoresist layer is formed on the surface of the first positive photoresist layer;
[0011] A second exposure is performed, wherein the second exposure uses a second exposure dose, which is less than the first exposure dose;
[0012] The first positive photoresist layer and the second positive photoresist layer are developed once to form an injection window;
[0013] Ion implantation is performed on the substrate through the implantation window.
[0014] As an optional implementation, at least part of the bottom of the deep trench forms the injection area;
[0015] The first exposure is performed using a mask having an exposure window aligned with the area to be injected.
[0016] The second exposure is performed using the mask, with the exposure window of the mask aligned with the area to be injected.
[0017] As an optional implementation, the first exposure dose is greater than or equal to 5000 mJ / cm².
[0018] As an optional implementation, the second exposure dose is less than or equal to 2500 mJ / cm².
[0019] As an optional implementation, the first positive photoresist layer includes a first portion and a second portion;
[0020] The first portion covers the mesa region of the substrate, and the second portion covers the inner surface of the deep trench. The thickness Ta of the first portion and the thickness Tb of the second portion satisfy: Ta < Tb / 5.
[0021] As an optional implementation, the thickness Tc of the second positive photoresist layer satisfies the same condition as the thickness Ta of the first portion: Tc > 3 × Ta.
[0022] As an optional implementation, along the depth direction of the deep trench, the first positive photoresist layer includes a first adhesive layer and a second adhesive layer connected together.
[0023] At least a portion of the first adhesive layer is located at the bottom of the deep trench, and the second adhesive layer is located above the first adhesive layer, wherein the refractive index of the first adhesive layer is greater than that of the second adhesive layer.
[0024] As an optional implementation, before forming the first positive photoresist layer on the surface of the substrate, the method further includes:
[0025] A light guiding structure is formed on the inner wall of the deep trench, which is used to guide the incident light beam during the first exposure to the bottom of the deep trench.
[0026] As an optional implementation, the light guiding structure includes a light reflecting layer for reflecting the incident light during the first exposure to the bottom of the deep trench.
[0027] As an alternative implementation, the light-guiding structure is removed before ion implantation of the substrate through the implantation window.
[0028] The ion implantation method for semiconductor structures provided in this application first utilizes a high-dose initial exposure to ensure light penetration into the deep trench, fully exposing the first layer of positive photoresist at the bottom of the trench, overcoming the development residue problem caused by insufficient light in traditional single exposures. Secondly, a second layer of photoresist is coated on the exposed first layer, followed by a lower-dose second exposure, which precisely defines the patterned area to be developed. Finally, a single development step forms a residue-free, size-controllable implantation window at the bottom of the deep trench. This method, through a process sequence of two coatings, two exposures, and one development step, solves the problem of difficult development at the bottom of deep trenches, achieving precise and reliable ion implantation at the bottom of deep trenches. Attached Figure Description
[0029] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.
[0030] Figure 1 This is a schematic diagram of the photoresist layer under normal exposure intensity in the prior art;
[0031] Figure 2 Schematic diagram of photoresist layer development in existing technology Figure 1 ;
[0032] Figure 3 This is a schematic diagram of the photoresist layer under enhanced exposure intensity in the prior art.
[0033] Figure 4 Schematic diagram of photoresist layer development in existing technology Figure 2 ;
[0034] Figure 5 A schematic flowchart of an ion implantation method for a semiconductor structure provided in an embodiment of this application;
[0035] Figure 6 This is a schematic diagram of the photosensitivity of the first positive photoresist layer after its first exposure, as shown in an embodiment of this application.
[0036] Figure 7 This is a schematic diagram of the photosensitive state of the second positive photoresist layer after a second exposure, as shown in an embodiment of this application.
[0037] Figure 8 This is a schematic diagram showing the development of the first positive photoresist layer and the second positive photoresist layer in the embodiments of this application;
[0038] Figure 9This is a schematic diagram of ion implantation of the substrate through an implantation window in an embodiment of this application;
[0039] Figure 10 This is a schematic diagram of the structure of the first positive photoresist layer, including a first adhesive layer and a second adhesive layer, in an embodiment of this application.
[0040] Figure 11 This is a schematic diagram of the structure in which the inner wall of the deep trench in this embodiment has a light-guiding structure.
[0041] Explanation of reference numerals in the attached figures:
[0042] 100. Substrate; 101. Deep trench;
[0043] 200, Photoresist layer; 201, Photosensitive area; 202, Developing area;
[0044] 210, First positive photoresist layer; 2101, First photoresist layer; 2102, Second photoresist layer;
[0045] 211. Part One;
[0046] 212. Part Two;
[0047] 220. Second positive photoresist layer;
[0048] 230. Injection window;
[0049] 300. Mask;
[0050] 400. Light guiding structure.
[0051] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation
[0052] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the embodiments of this application.
[0053] In the embodiments of this application, the terms "upper," "lower," "inner," "middle," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are mainly for better describing the embodiments of this application and their implementations, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation. Furthermore, some of the above terms may be used to indicate other meanings besides orientation or positional relationship; for example, the term "upper" may also be used in some cases to indicate a certain dependency or connection relationship. For those skilled in the art, the specific meaning of these terms in the embodiments of this application can be understood according to the specific circumstances.
[0054] Furthermore, the terms "set up," "connect," and "fix" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this disclosure according to the specific circumstances.
[0055] The terms "first," "second," "third," "fourth," etc. (if present) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the present application described herein can be implemented, for example, in orders other than those illustrated or described herein.
[0056] In this application, the terms "exemplarily" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplarily" or "for example" in this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplarily" or "for example" is intended to present the relevant concepts in a specific manner.
[0057] In related technologies, positive photoresist is used as a mask when performing ion implantation at the bottom of deep trenches in semiconductor devices. Under normal exposure intensity, the photosensitive area 201 after exposure of the photoresist layer 200 is as follows: Figure 1 As shown, the developed area 202 after development is as follows Figure 2 As shown. Because the exposure light cannot fully reach the bottom of the deep trench and react with the photoresist, photoresist residue remains at the bottom of the deep trench after development, preventing the formation of an effective injection window. If the exposure intensity is increased to remove the residue, the photosensitive area 201 after exposure of the photoresist layer 200 will be as shown. Figure 3As shown, the developed area 202 after development is as follows Figure 4 As shown. At this point, due to the reflection and diffraction effects of light within the deep trenches, the developed pattern differs significantly from the design layout, leading to loss of control over critical dimensions. When negative photoresist is used as the mask, the developer can easily cause lateral etching of the photoresist at the bottom of the deep trenches, resulting in photoresist detachment or mask pattern deformation, which also makes precise ion implantation impossible.
[0058] In view of this, embodiments of this application provide an ion implantation method for semiconductor structures to solve the process problems caused by incomplete photoresist development or mask structure failure when performing ion implantation on the bottom of deep trenches.
[0059] The ion implantation method for the semiconductor structure includes: providing a substrate having a deep trench; forming a first positive photoresist layer on the surface of the substrate; performing a first exposure using a first exposure dose to expose the first positive photoresist layer at the bottom of the deep trench; forming a second positive photoresist layer on the surface of the first positive photoresist layer; performing a second exposure using a second exposure dose less than the first exposure dose; performing a first development on the first and second positive photoresist layers to form an implantation window; and performing ion implantation on the substrate through the implantation window.
[0060] The ion implantation method for semiconductor structures disclosed in this application first utilizes a high-dose initial exposure to ensure light penetration into the deep trench, fully exposing the first layer of positive photoresist at the bottom of the trench, thus overcoming the problem of residual development caused by insufficient light in traditional single exposures. Secondly, a second layer of photoresist is coated onto the exposed first layer, followed by a lower-dose second exposure, which precisely defines the patterned area to be developed. Finally, a single development step forms a residue-free, size-controllable implantation window at the bottom of the deep trench. This method, through a process sequence of two coatings, two exposures, and one development step, solves the problem of difficult development at the bottom of deep trenches, achieving precise and reliable ion implantation at the bottom of deep trenches.
[0061] The technical solution of this application will be described in detail below with reference to the accompanying drawings and specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.
[0062] Combination Figure 5 As shown in the figure, this application provides an ion implantation method for a semiconductor structure, including the following steps:
[0063] S101, Provide a substrate having deep trenches;
[0064] S102. A first positive photoresist layer is formed on the surface of the substrate;
[0065] S103. Perform the first exposure. The first exposure uses the first exposure dose to expose the first positive photoresist layer at the bottom of the deep trench.
[0066] S104. A second positive photoresist layer is formed on the surface of the first positive photoresist layer;
[0067] S105. Perform a second exposure, using a second exposure dose that is less than the first exposure dose.
[0068] S106. The first positive photoresist layer and the second positive photoresist layer are developed once to form an injection window;
[0069] S107. Ion implantation is performed on the substrate through the implantation window.
[0070] Specifically, the method first provides a substrate 100 on which a deep trench 101 is formed. This deep trench 101 can be a deep trench structure used to form power semiconductor devices such as insulated gate bipolar transistors (IGBTs), typically characterized by a large aspect ratio, for example, a depth-to-width ratio greater than 10:1. In subsequent processes, ion implantation, such as P-type doping, is performed at the bottom of the deep trench 101 to optimize the electric field distribution of the device during reverse breakdown.
[0071] Next, a first positive photoresist layer 210 is formed on the surface of the substrate 100. This first positive photoresist layer 210 covers the mesa region of the substrate 100 and the inner surface of the deep trench 101, including the sidewalls and bottom of the deep trench 101. Due to the presence of the deep trench 101, the thickness of the first positive photoresist layer 210 inside the deep trench 101 is typically greater than its thickness in the mesa region. The formation of this first positive photoresist layer 210 serves to provide photosensitive material for the subsequent first exposure and as a base layer for subsequent processes.
[0072] Combination Figure 6 As shown, a first exposure is then performed. This first exposure uses a first exposure dose, which is set to a relatively high value, for example, greater than 5000 mJ / cm². It is understandable that in conventional single-exposure processes, due to light attenuation within the deep trench 101, the photoresist at the bottom of the deep trench 101 often fails to receive sufficient exposure, resulting in residue after development. The embodiment of this application uses such a high exposure dose to ensure that even for a deep trench 101 with a relatively large depth, light can fully penetrate and reach the bottom of the deep trench 101, allowing the first positive photoresist layer 210 located at the bottom of the deep trench 101 to be sufficiently photosensitive.
[0073] Combination Figure 7As shown, after the first exposure, a second positive photoresist layer 220 is formed on the surface of the first positive photoresist layer 210. This second positive photoresist layer 220 covers the first positive photoresist layer 210 that has undergone the first exposure. Forming this second positive photoresist layer 220 provides new photosensitive material for the subsequent second exposure, protects the area already exposed in the first exposure using its thickness, and provides a patterning basis for accurately defining the injection window 230.
[0074] Subsequently, a second exposure is performed. This second exposure uses a second exposure dose, which is less than the first exposure dose used in the first exposure. For example, the second exposure dose can be less than 2500 mJ / cm². The second exposure allows for precise patterning of the area where the injection window 230 needs to be formed. Since the bottom of the deep trench 101 has already been sufficiently photosensitive through the first high-dose exposure, the second exposure only needs to expose the second positive photoresist layer 220 with a lower dose to precisely define the boundary of the area to be developed 202, thereby avoiding pattern distortion or loss of critical dimensions due to overexposure.
[0075] Combination Figure 8 As shown, after the two exposures are completed, the first positive photoresist layer 210 and the second positive photoresist layer 220 are developed once. Since the first high-dose exposure has sufficiently exposed the first positive photoresist layer 210 at the bottom of the deep trench 101, and the second low-dose exposure has precisely defined the pattern, a single development operation can simultaneously remove the exposed first positive photoresist layer 210 at the bottom of the deep trench 101 and the corresponding area of the second positive photoresist layer 220, thereby forming a clear, residue-free injection window 230 at the bottom of the deep trench 101. The size and position of this injection window 230 are precisely controlled by the pattern from the second exposure.
[0076] Combination Figure 9 As shown, finally, ion implantation is performed on the substrate 100 through the implantation window 230 formed by the above development. The type and dose of ions implanted can be selected according to the device requirements. For example, for IGBT devices, P-type doping implantation (such as boron ion implantation) can be performed to achieve doping at the bottom of the deep trench 101, thereby optimizing the electric field distribution of the device and improving the reverse breakdown voltage performance.
[0077] Through the above methods, the embodiments of this application achieve the following technical effects: First, by using a high-dose first exposure, the positive photoresist at the bottom of the deep trench 101 is ensured to be fully photosensitive, fundamentally solving the problem of residual development caused by insufficient light in traditional positive photoresist processes. Second, by using a second low-dose exposure and a second coating, the pattern of the implantation window 230 is precisely defined, avoiding pattern distortion caused by overexposure. Then, the entire development process can be completed in one development step, simplifying the process flow. Finally, the entire process uses positive photoresist, avoiding structural stability problems such as photoresist detachment or mask pattern deformation caused by lateral etching of the developer when using negative photoresist. Therefore, the method provided by the embodiments of this application can accurately and reliably form the implantation window 230 at the bottom of the deep trench 101, thereby achieving high-quality ion implantation.
[0078] In some embodiments, at least a portion of the bottom of the deep trench 101 is formed into a region to be implanted. This region to be implanted is a specific location where localized ion implantation is required. For example, in an insulated-gate bipolar transistor (IGBT) device, this region to be implanted corresponds to the bottom region of the deep trench 101 where P-type doping is required to optimize the electric field distribution at the bottom of the deep trench 101 during reverse breakdown. By performing localized ion implantation in this specific region, the electric field distribution inside the device can be precisely controlled, thereby improving the breakdown voltage and reliability of the device.
[0079] To achieve precise graphical representation of the area to be injected, a mask 300 is used during the first exposure. This mask 300 has an exposure window whose shape and position correspond to the area to be injected.
[0080] During the first exposure, the mask 300 is positioned above the first positive photoresist layer 210, and the exposure window of the mask 300 is aligned with the area to be implanted. In this way, the exposure light can only illuminate the first positive photoresist layer 210 below through the exposure window, thereby achieving a high-dose first exposure in the area corresponding to the area to be implanted at the bottom of the deep trench 101. Because the first exposure uses a high exposure dose, the first positive photoresist layer 210 in this area is fully exposed to light, while other areas of the mask 300 block light, protecting the photoresist in non-implanted areas from exposure.
[0081] During the second exposure, the same mask 300 is used, and its exposure window is aligned again with the area to be injected. Since the second exposure uses a lower exposure dose, its purpose is to precisely define the boundary of the injection window 230, rather than subjecting the bottom of the deep trench 101 to another strong exposure. By aligning the exposure window of the mask 300 with the area to be injected, the second exposure exposes the second positive photoresist layer 220 only within the area corresponding to the injection area, thereby precisely defining the patterned area to be removed during subsequent development.
[0082] By using the same mask 300 for both exposures and aligning it with the area to be injected, it is ensured that the patterns defined by the first high-dose exposure and the second low-dose exposure remain highly consistent in spatial position. This consistency is crucial for the accuracy of the final injection window 230.
[0083] In a subsequent development process, because the first high-dose exposure has sufficiently exposed the first positive photoresist layer 210 at the bottom of the deep trench 101 corresponding to the area to be injected, the photoresist in that area can be effectively removed during development. Combined with... Figure 6 and Figure 7 As shown, although the light from the first high-dose exposure may cause a significant deviation between the developed pattern and the design layout due to reflection and diffraction effects within the deep trench 101, the second low-dose exposure can accurately redefined the boundary of this area. Through the synergistic effect of the two exposures, an implantation window 230 that perfectly matches the exposure window pattern of the mask 300 can be formed at the bottom of the deep trench 101 after development. This implantation window 230 has advantages such as precise positioning, clear boundaries, and no photoresist residue, thus providing a high-quality mask opening for subsequent localized ion implantation.
[0084] By employing the exposure method described above for aligning the mask 300, this embodiment of the application achieves a precise graphical definition of the injection area at the bottom of the deep trench 101. This method not only ensures the positional accuracy of the injection window 230, making it highly consistent with the design layout, but also simplifies the process steps and reduces process errors caused by mask 300 replacement or alignment deviations through the reuse of the same mask 300.
[0085] In some embodiments, the first exposure dose is greater than or equal to 5000 mJ / cm². In the fabrication of the deep trench 101 structure, because the deep trench 101 has a large aspect ratio, for example, a depth-to-width ratio greater than 10:1, light undergoes significant attenuation as it passes through the interior of the deep trench 101. If the exposure dose is insufficient, the light will not reach the bottom of the deep trench 101 sufficiently, resulting in incomplete photoresist exposure of the first positive photoresist layer 210 at the bottom of the deep trench 101. This leads to photoresist residue during subsequent development, hindering ion implantation.
[0086] By setting the first exposure dose to greater than or equal to 5000 mJ / cm², the attenuation of light in the deep trench 101 can be effectively compensated, ensuring that even for a deep trench 101 with a large depth, the positive photoresist at the bottom can obtain sufficient light energy, thereby achieving full and complete photosensitiveness, laying the foundation for the subsequent formation of a residue-free injection window 230.
[0087] In some embodiments, the second exposure dose is less than or equal to 2500 mJ / cm². The second exposure is used to precisely define the pattern of the injection window 230, rather than to subject the bottom of the deep trench 101 to another strong exposure. If the second exposure dose is too high, it may cause the already coated second positive photoresist layer 220 to be overexposed, resulting in blurred edges of the pattern after development, loss of critical dimensions, and may even adversely affect the underlying photosensitive first positive photoresist layer 210, causing the size of the injection window 230 to deviate from the design value.
[0088] By limiting the second exposure dose to less than or equal to 2500 mJ / cm², it is possible to ensure that the second positive photoresist layer 220 is sufficiently photosensitive to form a clear pattern boundary, while avoiding pattern distortion caused by overexposure. This low-dose exposure works in conjunction with the first high-dose exposure to achieve precise control over the injection window 230 at the bottom of the deep trench 101.
[0089] It should be noted that the specific numerical ranges of the first and second exposure doses mentioned above are preferred ranges determined based on the typical dimensions of the deep trench 101 structure, the photosensitivity of the photoresist, and process experience. In practical applications, the above dose ranges can be appropriately adjusted according to factors such as the specific aspect ratio of the deep trench 101, the type and thickness of the photoresist, etc. For example, for a deep trench 101 with a larger aspect ratio, the lower limit of the first exposure dose can be appropriately increased; while for a photoresist with higher photosensitivity, the upper limit of the second exposure dose can be appropriately decreased.
[0090] By separately limiting the exposure doses of the two exposures as described above, this embodiment of the application achieves stepwise control over the photoresist photosensitive state at the bottom of the deep trench 101. The first high-dose exposure ensures sufficient photosensitive exposure at the bottom of the deep trench 101, solving the problem of residual development; the second low-dose exposure enables precise definition of the implantation window 230 pattern, avoiding pattern distortion. The synergistic effect of the two exposures ensures that the implantation window 230 formed at the bottom of the deep trench 101 has neither photoresist residue nor a precisely controllable critical size, thus providing a high-quality mask opening (i.e., implantation window 230) for subsequent local ion implantation processes.
[0091] Combination Figure 7 As shown, in some embodiments, the first positive photoresist layer 210 includes a first portion 211 and a second portion 212. The first portion 211 covers the mesa region of the substrate 100, i.e., the raised surface region between the deep trenches 101; the second portion 212 covers the inner surface of the deep trenches 101, including the sidewalls and bottom of the deep trenches 101. Due to the presence of the deep trenches 101, during photoresist coating, the photoresist accumulates inside the deep trenches 101 due to surface tension and flowability, resulting in the thickness Tb of the second portion 212 typically being greater than the thickness Ta of the first portion 211.
[0092] Specifically, in the embodiments of this application, the thickness Ta of the first part 211 and the thickness Tb of the second part 212 satisfy: Ta < Tb / 5, that is, the thickness of the photoresist covering the mesa area of the first part 211 should be less than one-fifth of the thickness of the photoresist covering the inner surface of the deep trench 101.
[0093] During the first high-dose exposure, if the photoresist thickness in the mesa area is too thick due to the large exposure dose, the photoresist in that area will also be fully exposed to light, causing the photoresist in the mesa area to be accidentally removed during subsequent development, thereby compromising the mask protection effect of the non-injection area.
[0094] By controlling the thickness of the first part of the mesa region to a relatively thin level, the overexposure effect of high-dose exposure on the mesa region photoresist can be effectively reduced, allowing the photoresist in the mesa region to be retained after development and continue to play a mask protection role.
[0095] Specifically, in combination Figure 6 As shown, during the first high-dose exposure, the light within the deep trench 101 may experience reflection and diffraction effects, leading to a significant deviation between the pattern formed by the unexposed portion of the second part 212 and the design layout. However, combined with... Figure 7As shown, after the second positive photoresist layer 220 is set, through the second low-dose exposure, the boundary of this region can be accurately re-defined in the second positive photoresist layer 220, thereby effectively compensating for the pattern deviation caused by the optical effect in the first exposure and ensuring that the injection window 230 after the final development is highly consistent with the design layout.
[0096] For the photoresist of the second part 212 inside the deep trench 101, due to its relatively large thickness and being located at the bottom of the deep trench 101, a relatively high exposure dose is required to achieve sufficient photosensitivity. Therefore, the thickness Tb of the second part 212 photoresist can be relatively large to ensure that the photoresist at the bottom of the deep trench 101 can obtain sufficient photosensitive amount during the first high-dose exposure.
[0097] It should be noted that the above thickness relationship Ta < Tb / 5 is a preferred limited range. In the actual process, this thickness relationship can be achieved by adjusting the coating process parameters (such as the rotation speed of spin coating, the viscosity of the photoresist, etc.). For example, using a lower rotation speed or a higher viscosity photoresist can increase the accumulation amount of the photoresist inside the deep trench 101, thereby increasing Tb; while using a higher rotation speed or a lower viscosity photoresist can reduce the thickness of the photoresist in the mesa area, thereby reducing Ta. By optimizing the coating process, the thickness distribution of the first positive photoresist layer 210 can be precisely controlled to meet the above relationship.
[0098] Through the above limitation on the thickness distribution of the first positive photoresist layer 210, the embodiments of the present application achieve differential control of the photosensitive states of the photoresist in the mesa area and inside the deep trench 101. The thin glue layer in the mesa area effectively avoids the overexposure problem caused by high-dose exposure and protects the mask integrity of the non-injection area; while the thick glue layer inside the deep trench 101 ensures sufficient photosensitivity of the bottom photoresist and provides additional protection for the sidewalls of the deep trench 101.
[0099] Combined with Figure 7 As shown, in some embodiments, the thickness Tc of the second positive photoresist layer 220 and the thickness Ta of the first part 211 satisfy: Tc > 3×Ta.
[0100] During the second exposure and subsequent development, the second positive photoresist layer 220 not only precisely defines the pattern of the injection window 230, but also plays a crucial role in protecting the underlying first positive photoresist layer 210 and the surface of the substrate 100 in the non-injection area. Especially during the second exposure, although a lower exposure dose is used, some stray or reflected light may still exist, interfering with the non-exposed areas. By setting the thickness Tc of the second positive photoresist layer 220 to be more than three times the thickness Ta of the mesa portion of the first positive photoresist layer 210, a sufficiently thick photoresist mask layer can be formed. This effectively absorbs and blocks stray light, preventing it from penetrating to the underlying first positive photoresist layer 210, thereby avoiding accidental exposure or development of the photoresist in the non-injection area and ensuring the integrity and accuracy of the mask pattern.
[0101] After development to form the implantation window 230, the second positive photoresist layer 220 and the first positive photoresist layer 210 together serve as the ion implantation mask in the subsequent ion implantation process. For the deep trench 101 structure, during ion implantation, implanted ions may be incident at a certain angle or diffuse laterally due to scattering. If the mask layer thickness is insufficient, implanted ions may penetrate the mask layer and enter the substrate 100 in the non-implantation region, leading to unintended doping and affecting the electrical performance of the device. By setting the thickness Tc of the second positive photoresist layer 220 to be sufficiently large, it can be ensured that the mask layer has sufficient blocking ability to effectively prevent implanted ions from penetrating the mask, thereby achieving precise control over the ion implantation region.
[0102] The second positive photoresist layer 220 is coated on top of the first positive photoresist layer 210, which has already undergone its first exposure. After the first high-dose exposure, the surface properties of the first positive photoresist layer 210 may change, such as hardening or cross-linking. If the thickness of the second positive photoresist layer 220 is too thin, it may not form a good interface with the underlying first positive photoresist layer 210, making it prone to peeling or detachment during subsequent development or cleaning. By setting the thickness Tc of the second positive photoresist layer 220 to be greater than three times Ta, sufficient mechanical strength and adhesion can be ensured, thereby guaranteeing the stability of the entire photoresist stack structure.
[0103] It should be noted that the thickness relationship Tc>3×Ta described above is a preferred range. In actual processes, this thickness relationship can be achieved by adjusting the process parameters of the second coating (such as the spin coating speed, the viscosity of the photoresist, the number of coatings, etc.). For example, using a lower spin speed or multiple coatings can increase the thickness of the second positive photoresist layer 220.
[0104] By limiting the thickness of the second positive photoresist layer 220 as described above, the thicker second positive photoresist layer 220 provides reliable mask protection for the entire process, ensuring the accuracy of the implantation window 230 and the integrity of the non-implantation area, thereby helping to achieve high-precision and high-reliability local ion implantation at the bottom of the deep trench 101.
[0105] Combination Figure 10 As shown, in some embodiments, along the depth direction of the deep trench 101, the first positive photoresist layer 210 is not a single uniform material layer, but includes a first photoresist layer 2101 and a second photoresist layer 2102 connected together. At least a portion of the first photoresist layer 2101 is located at the bottom of the deep trench 101, while the second photoresist layer 2102 is located above the first photoresist layer 2101, i.e., closer to the opening of the deep trench 101. The first photoresist layer 2101 and the second photoresist layer 2102 differ in material properties, specifically: the refractive index of the first photoresist layer 2101 is greater than that of the second photoresist layer 2102.
[0106] In the deep trench 101 structure, light entering from the opening of the deep trench 101 needs to pass through the relatively deep trench 101 to reach the bottom. Due to the large depth-to-width ratio of the deep trench 101, the light undergoes significant attenuation and scattering during propagation, resulting in insufficient light intensity at the bottom of the deep trench 101. By setting a first photoresist layer 2101 with a higher refractive index at the bottom of the deep trench 101, the refraction and focusing effects of light can be utilized to more effectively guide and converge the incident light beam to the bottom of the deep trench 101. Specifically, when light enters the first photoresist layer 2101 with a higher refractive index from the second photoresist layer 2102 with a lower refractive index, the light is deflected towards the normal direction, thereby changing the propagation path. This redirects light that might otherwise be scattered to the sidewalls of the deep trench 101 to the bottom of the deep trench 101. This optical waveguide effect can effectively increase the light intensity at the bottom of the deep trench 101, ensuring sufficient photoresist exposure at the bottom.
[0107] Specifically, the refractive index gradient structure can be achieved by using multilayer coating or material doping when coating the first positive photoresist layer 210. For example, a high-refractive-index photoresist material (such as a positive photoresist doped with high-refractive-index nanoparticles) can be deposited at the bottom of the deep trench 101 first, and then a positive photoresist with a conventional refractive index can be coated. Alternatively, the photoresist formulation can be adjusted to allow a refractive index gradient to form naturally during the curing process. Regardless of the method used, this refractive index gradient structure is compatible with existing photolithography processes without introducing additional complex equipment or steps.
[0108] It should be noted that in practical applications, the refractive index difference between the first adhesive layer 2101 and the second adhesive layer 2102 can be further optimized to match deep trench 101 structures with different aspect ratios and sizes. For example, for deep trench 101 with a larger aspect ratio, the refractive index difference between the first adhesive layer 2101 and the second adhesive layer 2102 can be appropriately increased to enhance the optical waveguide effect; while for deep trench 101 with a smaller aspect ratio, the refractive index difference can be appropriately decreased to avoid uneven light intensity distribution caused by over-focusing.
[0109] By designing the refractive index gradient structure within the first positive photoresist layer 210 as described above, this embodiment of the application achieves active control over the beam propagation path within the deep trench 101. The high-refractive-index first photoresist layer 2101 is located at the bottom of the deep trench 101, effectively enhancing the bottom light intensity and improving exposure uniformity. This refractive index gradient structure further enhances the control over the development effect at the bottom of the deep trench 101 by the technical solution of this application, providing support for achieving high-precision, high-uniformity local ion implantation.
[0110] It should be noted that, in order to ensure the permeability of the developer, the interface between the first photoresist layer 2101 and the second photoresist layer 2102 of the first positive photoresist layer 210 can be designed as a gradient transition structure to avoid the developer from increasing the permeation resistance due to the sudden change in refractive index at the interface, thereby ensuring the uniformity of the development process.
[0111] It should also be noted that the first positive photoresist layer 210 and the second positive photoresist layer 220 can be configured by deposition, coating, spin coating, etc.
[0112] Specifically, a spin coating process can be used, where the spin coating speed, adhesive viscosity, and drop volume are controlled to ensure that the photoresist is uniformly covered on the surface of the substrate 100 and inside the deep trench 101. Alternatively, a spray coating process can be used, where the photoresist is atomized and sprayed onto the surface of the substrate 100 using a nozzle, which is suitable for complex morphologies with high aspect ratio deep trenches 101. Thin film deposition processes such as chemical vapor deposition or atomic layer deposition can also be used to form a photoresist film on the surface of the substrate 100 through a gas phase reaction, which is suitable for scenarios with high requirements for film thickness uniformity and step coverage.
[0113] Furthermore, for multilayer photoresist structures (e.g., a first positive photoresist layer 210 composed of a first resist layer 2101 and a second resist layer 2102), multiple spin-coating or alternating deposition methods can be used to first form the first resist layer 2101, and then form the second resist layer 2102 on top of it. Regardless of the method used, it should be ensured that the photoresist layers can fully fill or cover the bottom and sidewalls of the deep trench 101, and that there is good interfacial adhesion and process compatibility between the layers, so as to achieve the expected pattern transfer effect in subsequent exposure and development processes.
[0114] Combination Figure 11 As shown, in some embodiments, before forming the first positive photoresist layer 210 on the surface of the substrate 100, a pre-step is added: forming a light guiding structure 400 on the inner wall of the deep trench 101. The function of the light guiding structure 400 is to effectively guide the incident light beam during the first exposure to the bottom of the deep trench 101, thereby increasing the light intensity at the bottom of the deep trench 101 and improving the photosensitivity of the bottom photoresist.
[0115] As previously mentioned, due to the large aspect ratio of the deep trench 101, light undergoes significant attenuation and scattering as it passes through the interior of the deep trench 101, resulting in a much lower light intensity at the bottom of the deep trench 101 compared to its opening. Even with a high-dose first exposure, the light intensity at the bottom of the deep trench 101, with its extremely large aspect ratio, may still be insufficient to fully expose the photoresist. By pre-forming a light-guiding structure 400 on the inner wall of the deep trench 101, the propagation path of the light can be actively altered, collecting and guiding light that might otherwise be scattered to the sidewalls or fail to reach the bottom to the bottom of the deep trench 101, thereby effectively increasing the light intensity at the bottom and ensuring sufficient exposure of the photoresist thereon.
[0116] Without the light-guiding structure 400, extremely high exposure doses (e.g., well above 5000 mJ / cm²) are often required to ensure sufficient light exposure at the bottom of the deep trench 101. However, excessively high exposure doses can lead to a series of side effects, such as overexposure of the photoresist in the mesa area, hardening or cross-linking of the photoresist, and increased equipment load. By introducing the light-guiding structure 400, the light intensity at the bottom of the deep trench 101 can be effectively increased without significantly increasing the exposure dose, thereby reducing dependence on high exposure doses and improving process flexibility and compatibility.
[0117] The light guiding structure 400 can be implemented in various ways. For example, the light guiding structure 400 may include a light conditioning layer formed on the inner wall of the deep trench 101. The material of the light conditioning layer can be a high-refractive-index dielectric material (such as silicon nitride, titanium oxide, etc.) or a high-reflectivity metallic material (such as aluminum, silver, etc.). When light is incident on the light conditioning layer, it is refracted or reflected, thereby changing the propagation direction and guiding more light to the bottom of the deep trench 101. Alternatively, the light guiding structure 400 may include a periodic grating structure formed on the inner wall of the deep trench 101. This grating structure can disperse and guide the incident light beam to the bottom of the deep trench 101 through diffraction, achieving a more uniform light intensity distribution.
[0118] It should be noted that the formation process of the light-guiding structure 400 should be compatible with the subsequent photoresist coating process. For example, after the deep trench 101 is etched, a light-modifying material can be deposited on the inner wall of the deep trench 101 using processes such as chemical vapor deposition (CVD), physical vapor deposition (PVD), or atomic layer deposition (ALD). The thickness of this light-modifying layer should be controlled within an appropriate range to avoid overfilling of the deep trench 101 or affecting the uniformity of subsequent photoresist coating. Furthermore, after the first exposure, the light-guiding structure 400 can be selectively retained or removed, depending on its impact on subsequent processes.
[0119] By forming a light-guiding structure 400 on the inner wall of the deep trench 101 as described above, the light-guiding structure 400 of this embodiment guides the incident light beam to the bottom of the deep trench 101 through optical effects such as refraction, reflection, or diffraction. This significantly improves the photosensitivity of the bottom photoresist, reduces dependence on high exposure doses, and enhances the flexibility and adaptability of the process. The light-guiding structure 400, in conjunction with the aforementioned multiple exposure and layered coating techniques, can effectively improve the accuracy of ion implantation at the bottom of the deep trench 101.
[0120] In some embodiments, the light guiding structure 400 includes a light reflecting layer for reflecting incident light during the first exposure to the bottom of the deep trench 101.
[0121] The light-reflecting layer works through a reflection mechanism, which can directly reflect incident light back into the first positive photoresist layer 210, and the reflection angle is equal to the incident angle. By reasonably designing the shape and angle of the light-reflecting layer, the reflected light can be made to propagate in a direction closer to vertical downward, thereby more effectively guiding the light to the bottom of the deep trench 101.
[0122] The light-reflecting layer typically uses highly reflective materials, such as high-reflectivity metals like aluminum, silver, and gold, or a distributed Bragg reflector composed of alternating stacks of high- and low-refractive-index materials. When light shines on the surface of the light-reflecting layer, the vast majority of the light is reflected back into the first positive photoresist layer 210, with only a very small portion being absorbed or transmitted. This high reflectivity minimizes energy loss during light propagation, significantly increasing the light intensity at the bottom of the deep trench 101, thereby reducing dependence on high exposure doses and mitigating the risk of overexposure.
[0123] Specifically, the light-reflecting layer can be uniformly deposited on the inner wall of the deep trench 101 after etching using processes such as physical vapor deposition or chemical vapor deposition. For metallic reflective layers, sputtering or evaporation processes can be used; for dielectric reflective films, atomic layer deposition or plasma-enhanced chemical vapor deposition processes can be used. These deposition processes have good step coverage capabilities, and even for deep trenches 101 with a large depth-to-width ratio, a light-reflecting layer of uniform thickness can be formed on the sidewalls and bottom.
[0124] It should be noted that the reflectivity of the light-reflecting layer is closely related to its surface roughness and material properties. To obtain a better reflectivity, the surface of the light-reflecting layer can be made smooth to reduce scattering losses. Simultaneously, the thickness of the light-reflecting layer should be controlled within an appropriate range to ensure sufficient reflectivity while avoiding overfilling of the deep trench 101 or affecting the uniformity of subsequent photoresist coating. Furthermore, the shape of the light-reflecting layer can be designed as needed. For example, by controlling the deposition angle or subsequent etching processes, the light-reflecting layer can form a certain tilt angle on the sidewalls of the deep trench 101, thereby more effectively reflecting light to the bottom of the deep trench 101.
[0125] By setting the light-guiding structure 400 as a light-reflecting layer, this application provides a solution for efficiently guiding light through a reflection mechanism. The light-reflecting layer can more directly and efficiently reflect light back into the first positive photoresist layer 210 and guide it to the bottom of the deep trench 101, thereby further increasing the light intensity at the bottom of the deep trench 101 and reducing the dependence on high exposure doses.
[0126] In some embodiments, before ion implantation of the substrate 100 through the implantation window 230 formed by development, a pre-implantation step is included: removing the light-guiding structure 400. The purpose of this step is to prevent the light-guiding structure 400 from interfering with the penetration depth or distribution of implanted ions during subsequent ion implantation, thereby ensuring the accuracy and consistency of ion implantation.
[0127] The light-guiding structure 400 is formed on the inner wall of the deep trench 101. If ion implantation is performed directly in its presence, the implanted ions, after passing through the implantation window 230, must first penetrate the light-guiding structure 400 before entering the substrate 100. When the atomic number and density of the material of the light-guiding structure 400 differ from those of the substrate 100, the implanted ions experience additional energy loss and scattering as they pass through the light-guiding structure 400. This causes the energy and dose of the ions actually implanted into the substrate 100 to deviate from the design values, thus affecting the precise control of doping depth and concentration. Therefore, removing the light-guiding structure 400 before ion implantation can eliminate this interfering factor and ensure the accuracy of ion implantation.
[0128] It should be noted that the material selection for the light-reflecting layer should meet the requirements of compatibility with subsequent processes. For example, the light-reflecting layer material should not react with the oxide layer of the substrate 100 to avoid damage to the oxide layer in subsequent removal steps. After development to form the injection window 230, the light-reflecting layer can be cleanly removed by a selective etching process (such as wet etching) without damaging the underlying oxide layer of the substrate 100.
[0129] By removing the light-guiding structure 400 before ion implantation as described above, this embodiment of the application achieves precise timing control of the function of the light-guiding structure 400. The light-guiding structure 400 functions as a light guide during the exposure stage, enhancing the light intensity at the bottom of the deep trench 101. After development to form the implantation window 230, it is removed by selective etching without damaging the underlying substrate 100 oxide layer. Ion implantation is then performed, ensuring that the energy and dose of the implanted ions are not disturbed.
[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to depart from the spirit and scope of the technical solutions of the embodiments of this application.
Claims
1. An ion implantation method for a semiconductor structure, characterized in that, include: A substrate (100) is provided, the substrate (100) having a deep trench (101); A first positive photoresist layer (210) is formed on the surface of the substrate (100). A first exposure is performed, wherein the first exposure uses a first exposure dose to expose the first positive photoresist layer (210) at the bottom of the deep trench (101); A second positive photoresist layer (220) is formed on the surface of the first positive photoresist layer (210). A second exposure is performed, wherein the second exposure uses a second exposure dose that is less than the first exposure dose; The first positive photoresist layer (210) and the second positive photoresist layer (220) are developed once to form an injection window (230). Ion implantation is performed on the substrate (100) through the implantation window (230).
2. The ion implantation method for a semiconductor structure according to claim 1, characterized in that, At least part of the bottom of the deep trench (101) forms an injection area; The first exposure is performed using a mask (300) having an exposure window aligned with the area to be injected; The second exposure is performed using the mask (300), with the exposure window of the mask (300) aligned with the area to be injected.
3. The ion implantation method for a semiconductor structure according to claim 1, characterized in that, The first exposure dose is greater than or equal to 5000 mJ / cm².
4. The ion implantation method for a semiconductor structure according to claim 1, characterized in that, The second exposure dose is less than or equal to 2500 mJ / cm².
5. The ion implantation method for a semiconductor structure according to any one of claims 1-4, characterized in that, The first positive photoresist layer (210) includes a first portion (211) and a second portion (212); The first portion (211) covers the mesa region of the substrate (100), and the second portion (212) covers the inner surface of the deep trench (101). The thickness Ta of the first portion (211) and the thickness Tb of the second portion (212) satisfy: Ta < Tb / 5.
6. The ion implantation method for a semiconductor structure according to claim 5, characterized in that, The thickness Tc of the second positive photoresist layer (220) satisfies the same condition as the thickness Ta of the first portion (211): Tc > 3 × Ta.
7. The ion implantation method for a semiconductor structure according to claim 1, characterized in that, Along the depth direction of the deep trench (101), the first positive photoresist layer (210) includes a first adhesive layer (2101) and a second adhesive layer (2102) connected together. At least a portion of the first adhesive layer (2101) is located at the bottom of the deep trench (101), and the second adhesive layer (2102) is located above the first adhesive layer (2101), wherein the refractive index of the first adhesive layer (2101) is greater than the refractive index of the second adhesive layer (2102).
8. The ion implantation method for a semiconductor structure according to claim 1, characterized in that, Before forming the first positive photoresist layer (210) on the surface of the substrate (100), the method further includes: A light guiding structure (400) is formed on the inner wall of the deep trench (101), the light guiding structure (400) being used to guide the incident light beam during the first exposure to the bottom of the deep trench (101).
9. The ion implantation method for a semiconductor structure according to claim 8, characterized in that, The light guiding structure (400) includes a light reflecting layer for reflecting the incident light during the first exposure to the bottom of the deep trench (101).
10. The ion implantation method for a semiconductor structure according to claim 8, characterized in that, The light-guiding structure (400) is removed before ion implantation of the substrate (100) through the implantation window (230).