Low-temperature polycrystalline silicon thin film preparation method and low-temperature polycrystalline silicon thin film
By widening the grain boundaries through laser irradiation and oxidation treatment, and filling them with silicon nanoparticles to form covalent bonds, the passivation instability and hydrogen-induced defects of low-temperature polycrystalline silicon thin films were solved, thereby improving carrier mobility and thermal stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA MOBILE GROUP DESIGN INST
- Filing Date
- 2025-11-28
- Publication Date
- 2026-04-10
AI Technical Summary
The passivation effect of existing low-temperature polycrystalline silicon thin films is unstable and easily forms hydrogen-induced defects, such as hydrogen bubbles. It is difficult to achieve stable and efficient passivation of grain boundary defects without relying on high-temperature hydrogenation treatment.
In the process of preparing low-temperature polycrystalline silicon thin films, an amorphous silicon layer is transformed into a polycrystalline silicon layer by laser irradiation, and the grain boundaries are widened by oxidation treatment. Then, silicon nanoparticles are filled and dangling bonds at the grain boundaries are formed to form silicon-silicon covalent bonds.
This method achieves uniform, controllable widening of grain boundaries and stable passivation, avoiding thermal damage and bond dissociation problems caused by hydrogenation treatment, and improving carrier mobility and thermal stability of the thin film.
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Figure CN121843433A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of transistor manufacturing, and in particular to a low-temperature polysilicon thin film preparation method and a low-temperature polysilicon thin film. BACKGROUND
[0002] Low-temperature polysilicon (LTPS) is a material composed of polysilicon grains and grain boundaries, with a carrier mobility between amorphous silicon and single crystal silicon, and is widely used in the field of display devices. In recent years, with the development of radio frequency devices towards large area and high density integration, LTPS has been applied to high-frequency devices such as radio frequency switches due to its ability to be prepared on a glass substrate in a large area. However, the mobility of conventional LTPS is usually only 50-100 cm² / V·s, which is difficult to meet the demand for higher mobility of high-frequency radio frequency devices.
[0003] The main reason for the low mobility of LTPS is the presence of a large number of dangling bonds at the grain boundaries. These dangling bonds can trap carriers, form charged centers, reduce the effective carrier concentration, and induce band bending and potential barriers near the grain boundaries, hindering the movement of carriers between grains, thereby causing the mobility to decrease. To improve this phenomenon, the prior art usually adopts a hydrogenation treatment method, such as annealing in hydrogen, so that hydrogen atoms form Si-H bonds with dangling bonds, thereby passivating grain boundary defects.
[0004] However, the above hydrogenation treatment method has obvious limitations: first, hydrogenation treatment usually needs to be carried out in a high-temperature environment, which is easy to cause thermal damage to the amorphous silicon layer in LTPS, affecting the electrical properties; second, the Si-H bond has low binding energy and is easy to dissociate under strong electric field or high temperature conditions, resulting in unstable passivation effect; in addition, hydrogen atoms are small in size and easy to diffuse, which may gather at grain boundaries or defects to form hydrogen-induced defects (such as hydrogen bubbles), further affecting the reliability of the device.
[0005] Therefore, how to realize stable and efficient passivation of LTPS grain boundary defects without relying on high-temperature hydrogenation treatment has become a technical problem to be solved by the prior art. SUMMARY
[0006] The embodiments of the present application provide a low-temperature polysilicon thin film preparation method to solve the problem of unstable passivation effect and easy formation of hydrogen-induced defects (such as hydrogen bubbles) of the low-temperature polysilicon thin film prepared by using the existing low-temperature polysilicon thin film preparation method.
[0007] The embodiments of the present application adopt the following technical solutions: The application discloses a low-temperature polysilicon thin film preparation method, which comprises the following steps: forming a buffer layer on a substrate base plate; forming an amorphous silicon layer on the surface of the buffer layer far from the substrate base plate; performing laser irradiation on the amorphous silicon layer, and converting the amorphous silicon layer into a first polysilicon layer, wherein the first polysilicon layer comprises a plurality of crystal grains and crystal boundaries between the crystal grains; performing oxidation treatment on the first polysilicon layer, so as to widen the crystal boundaries between the crystal grains in the first polysilicon layer, and obtain a second polysilicon film layer; and adding a silicon nanoparticle solution on the surface of the second polysilicon film layer, and filling the silicon nanoparticles into the widened crystal boundaries, so that the silicon nanoparticles form silicon-silicon covalent bonds with dangling bonds at the crystal boundaries.
[0008] The above-mentioned at least one technical solution adopted by the embodiments of the application can achieve the following beneficial effects: The low-temperature polysilicon thin film preparation method provided by the embodiments of the application comprises the following steps: forming a buffer layer on a substrate base plate; forming an amorphous silicon layer on the surface of the buffer layer far from the substrate base plate; performing laser irradiation on the amorphous silicon layer, and converting the amorphous silicon layer into a first polysilicon layer, wherein the first polysilicon layer comprises a plurality of crystal grains and crystal boundaries between the crystal grains; performing oxidation treatment on the first polysilicon layer, so as to widen the crystal boundaries between the crystal grains in the first polysilicon layer, and obtain a second polysilicon film layer; and adding a silicon nanoparticle solution on the surface of the second polysilicon film layer, and filling the silicon nanoparticles into the widened crystal boundaries, so that the silicon nanoparticles form silicon-silicon covalent bonds with dangling bonds at the crystal boundaries. The low-temperature polysilicon thin film preparation method provided by the embodiments of the application can actively widen the crystal boundaries between the crystal grains in the first polysilicon layer by performing oxidation treatment on the first polysilicon layer, so that the width of the crystal boundaries can be accurately and controllably adjusted to a target size. The active and uniform lateral widening method is also effective for defect areas with high aspect ratios or non-planar structures, and ensures the consistency of the crystal boundary widening effect. In addition, the silicon nanoparticles are filled into the widened crystal boundaries, so that the silicon nanoparticles form silicon-silicon covalent bonds with the dangling bonds at the crystal boundaries. Compared with the Si-H bonds formed by hydrogenation treatment in the prior art, the silicon-silicon covalent bonds have higher bonding energy and thermal stability, and can effectively avoid the passivation failure problem caused by bond energy dissociation in a strong electric field or a high-temperature environment. BRIEF DESCRIPTION OF DRAWINGS
[0009] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and serve to explain the principles of the application, and do not limit the application in any way. In the drawings: Figure 1 A specific flowchart of a low-temperature polysilicon thin film preparation method provided by the embodiments of the application is shown in the figure; Figure 2A specific structure diagram of a first polycrystalline silicon layer after crystallization is provided in the embodiments of the present application; Figure 3 A cross-sectional diagram of a crystal grain / crystal boundary before silicon nanoparticle filling is provided; Figure 4 A cross-sectional diagram of a crystal grain / crystal boundary after silicon nanoparticle filling is provided; Figure 5 A state density distribution diagram of a low-temperature polycrystalline silicon thin film before and after silicon nanoparticle filling is provided. DETAILED DESCRIPTION
[0010] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described below in detail with the embodiments of the present application and corresponding drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.
[0011] Embodiment One The low-temperature polycrystalline silicon thin film preparation method provided in the embodiments of the present application is used to solve the problem that the passivation effect of the low-temperature polycrystalline silicon thin film prepared by using the existing low-temperature polycrystalline silicon thin film preparation method is unstable and hydrogen-induced defects (such as hydrogen bubbles) are easily formed.
[0012] The specific implementation flowchart of the low-temperature polycrystalline silicon thin film preparation method provided in the present application is shown in Figure 1 The method mainly includes the following steps: Step 11, forming a buffer layer on a substrate substrate; In the embodiments of the present application, a glass substrate substrate is provided. On the glass substrate substrate, a silicon nitride (SiN) layer is formed by a plasma enhanced chemical vapor deposition method, and the thickness is about 50 nm; then, a silicon dioxide (SiO2) layer is formed on the silicon nitride layer by the plasma enhanced chemical vapor deposition method, and the thickness is also about 50 nm. Thus, a SiN / SiO2 laminated buffer layer is formed.
[0013] The bottom silicon nitride layer can effectively block the upward diffusion of impurity ions (such as sodium ions) in the glass substrate in the subsequent high-temperature process; the top silicon dioxide layer has excellent interface compatibility with the subsequently formed polycrystalline silicon material, which helps to reduce interface defects.
[0014] Step 12, forming an amorphous silicon layer on the surface of the buffer layer obtained by performing step 11 away from the substrate, and converting the amorphous silicon layer into a first polycrystalline silicon layer by laser irradiation; On the surface of the buffer layer, a layer of amorphous silicon film is deposited by chemical vapor deposition method. In order to facilitate the effective widening and filling of the grain boundaries in the subsequent process, the thickness of the amorphous silicon layer is set to about 100 nm, and a solid-state laser with a wavelength of 532 nm is used to scan and irradiate the amorphous silicon layer. Since the 532 nm wavelength laser has a deeper absorption depth, it can more effectively realize the transformation of amorphous silicon to polycrystalline silicon.
[0015] After crystallization, a first polycrystalline silicon layer is obtained, as shown in Figure 2 Figure 2 It can be seen that the first polycrystalline silicon layer contains a plurality of crystal grains of different sizes and initial grain boundaries with a width of about 5-8 nm distributed between the crystal grains.
[0016] Step 13: The first polycrystalline silicon layer obtained by performing step 12 is subjected to an oxidation treatment to widen the grain boundaries between the crystal grains in the first polycrystalline silicon layer, and a second polycrystalline silicon film layer is obtained.
[0017] It should be noted that since the surface of the first polycrystalline silicon layer is naturally oxidized to form a very thin layer of silicon dioxide during the high-temperature crystallization process of step 12, the substrate after the crystallization treatment of step 12 can be rinsed in a diluted hydrofluoric acid solution before the oxidation treatment to remove the natural oxide layer formed on the surface during the crystallization treatment of step 12.
[0018] The substrate after the rinsing treatment is placed in a high-temperature baking oven and subjected to an oxidation treatment in oxygen to heat-oxidize the surface of the first polycrystalline silicon layer and the inner wall of the grain boundaries to form a new layer of silicon dioxide.
[0019] Then, the substrate is again rinsed in a hydrofluoric acid solution to remove the newly formed layer of silicon dioxide.
[0020] The above "oxidation-rinsing" cycle is repeated multiple times, and each cycle consumes silicon material at the edge of the grain boundary, thereby gradually widening the grain boundary laterally. By controlling the number of cycles, the width of the grain boundary is finally widened from the initial 5-8 nm to about 15 nm, thereby obtaining a second polycrystalline silicon film layer with widened grain boundaries.
[0021] Step 14: A silicon nanoparticle solution is added to the surface of the second polycrystalline silicon film layer obtained by performing step 13 to fill the widened grain boundaries with silicon nanoparticles.
[0022] First, a suspension solution containing silicon nanoparticles with a diameter of about 10 nm is configured. Since the width of the widened grain boundary is about 15 nm, the selection of 10 nm diameter particles can ensure that they enter and fill the grain boundary smoothly, while avoiding blockage due to too large particles or insufficient filling due to too small particles.
[0023] Then, the silicon nanoparticle solution is uniformly applied on the surface of the second polysilicon film layer by a spin coating method. After the spin coating is completed, the substrate is placed on a hot plate for low-temperature drying to remove the solvent in the solution, so that the silicon nanoparticles are stably filled in the grain boundaries.
[0024] In this process, the silicon atoms on the surface of the silicon nanoparticles react with the exposed dangling bonds at the grain boundaries to form stable silicon-silicon covalent bonds, thereby effectively passivating the grain boundary defects.
[0025] In the embodiments of the present application, the cross-sectional schematic diagram of the grain / grain boundary before filling is as shown in Figure 3 , and the cross-sectional schematic diagram of the grain / grain boundary after filling is as shown in Figure 4 , and the state density distribution of the low-temperature polysilicon thin film before and after filling the silicon nanoparticles is as shown in Figure 5 , and it can be known from Figure 5 that, compared with before filling, the defect state energy band located in the middle of the energy band structure is significantly reduced, and the corresponding grain boundary barrier is also reduced.
[0026] The low-temperature polysilicon thin film preparation method provided in the embodiments of the present application forms a buffer layer on a substrate; an amorphous silicon layer is formed on the surface of the buffer layer away from the substrate; the amorphous silicon layer is irradiated by laser to convert the amorphous silicon layer into a first polysilicon layer, the first polysilicon layer comprising a plurality of grains and grain boundaries between the grains; the first polysilicon layer is subjected to an oxidation treatment to widen the grain boundaries between the grains in the first polysilicon layer to obtain a second polysilicon film layer; a silicon nanoparticle solution is added to the surface of the second polysilicon film layer to fill the silicon nanoparticles into the widened grain boundaries, so that the silicon nanoparticles form silicon-silicon covalent bonds with the dangling bonds at the grain boundaries. The low-temperature polysilicon thin film preparation method provided in the embodiments of the present application, on the one hand, actively widens the grain boundaries between the grains in the first polysilicon layer by the oxidation treatment of the first polysilicon layer, which can accurately and controllably adjust the grain boundary width to a target size. This active and uniform lateral widening method is also effective for defect regions with high aspect ratio or non-planar structure compared with the hydrogenation treatment which relies on gas diffusion, ensuring the consistency of the grain boundary widening effect. On the other hand, by filling the silicon nanoparticles into the widened grain boundaries to form silicon-silicon covalent bonds with the dangling bonds at the grain boundaries, the silicon-silicon covalent bonds have higher binding energy and thermal stability than the Si-H bonds formed by the hydrogenation treatment in the prior art, which can effectively avoid the passivation failure problem of the low-temperature polysilicon thin film due to bond energy dissociation in a strong electric field or high-temperature environment.
[0027] Embodiment Two The main difference between this embodiment and Embodiment One is the application method of the silicon nanoparticle solution, and the other steps are the same.
[0028] In step 14, instead of using spin coating method, a solution of silicon nanoparticles is precisely printed onto the surface of the second polysilicon film layer using an inkjet printing device. This method has higher flexibility for local repair or patterning applications. After printing, the same drying process is performed to fill the silicon nanoparticles into the grain boundaries and form silicon-silicon covalent bonds with dangling bonds at the grain boundaries.
[0029] Embodiment Three This embodiment aims to illustrate that some process parameters can be adjusted within a certain range while ensuring the final grain boundary filling effect.
[0030] In step 12, the thickness of the amorphous silicon layer can be slightly higher or lower than 100 nm, for example, within the range of 80 nm to 120 nm, as long as its thickness is sufficient to support the subsequent formation of a moderate-width grain boundary.
[0031] In step 13, the target grain boundary width is not strictly limited to 15 nm, for example, it can be within the range of 12 nm to 18 nm. Accordingly, in step 14, the diameter of the selected silicon nanoparticles should always be smaller than the target grain boundary width, for example, for a 15 nm grain boundary, silicon nanoparticles with a diameter of 8 nm to 12 nm can be selected to ensure effective filling.
[0032] In step 14, in addition to spin coating and inkjet printing, the solution of silicon nanoparticles can also be added by other methods that can achieve uniform or selective distribution of the solution, such as dip coating, etc.
[0033] Embodiment Four This embodiment provides a low-temperature polysilicon thin film prepared by any of the methods in embodiments one to three. The thin film is characterized in that the grain boundaries are filled with silicon nanoparticles, and the silicon nanoparticles are combined with dangling bonds at the grain boundaries through stable silicon-silicon covalent bonds, thereby significantly reducing the defect state density and carrier potential barrier of the grain boundaries. Therefore, the thin film has higher carrier mobility, which is superior to the LTPS thin film obtained by traditional hydrogenation treatment.
[0034] Embodiment Five This embodiment provides a thin film transistor that uses the low-temperature polysilicon thin film described in embodiment four as an active layer. Due to the improvement of the mobility of the active layer, the thin film transistor has higher switching speed and driving capability.
[0035] The technical features of the above embodiments can be combined in any way. To make the description concise, not all possible combinations of the technical features in the above embodiments are described, but as long as the combinations of the technical features do not contradict, they should be considered within the scope of the present disclosure.
[0036] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of protection of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.
Claims
1. A method for preparing low-temperature polycrystalline silicon thin films, characterized in that, include: A buffer layer is formed on the substrate. An amorphous silicon layer is formed on the surface of the buffer layer away from the substrate. The amorphous silicon layer is irradiated with a laser to transform it into a first polycrystalline silicon layer. The first polycrystalline silicon layer contains a plurality of grains and grain boundaries located between the grains. The first polycrystalline silicon layer is oxidized to widen the grain boundaries between the grains in the first polycrystalline silicon layer, thereby obtaining a second polycrystalline silicon film layer. A silicon nanoparticle solution is added to the surface of the second polycrystalline silicon film to fill the widened grain boundaries with silicon nanoparticles, so that the silicon nanoparticles and the dangling bonds at the grain boundaries form silicon-silicon covalent bonds.
2. The method according to claim 1, characterized in that, The oxidation treatment of the first polycrystalline silicon layer to widen the grain boundaries between the grains in the first polycrystalline silicon layer, thereby obtaining the second polycrystalline silicon film layer, specifically includes: The first polycrystalline silicon layer is subjected to cyclic oxidation and etching to widen the grain boundaries between the grains in the first polycrystalline silicon layer, thereby obtaining a second polycrystalline silicon film layer.
3. The method according to claim 2, characterized in that, The cyclic oxidation and etching process on the first polysilicon layer specifically includes: The first polycrystalline silicon layer is oxidized to form an oxide layer on the surface and at the grain boundaries of the first polycrystalline silicon layer. The oxide layer was removed by rinsing with hydrofluoric acid solution. Repeat the oxidation and rinsing steps until the width of the grain boundary reaches the target size.
4. The method according to claim 1, characterized in that, The addition of a silicon nanoparticle solution to the surface of the second polycrystalline silicon film specifically includes: Spin-coat the silicon nanoparticle solution onto the surface of the second polycrystalline silicon film; or The silicon nanoparticle solution is inkjet printed on the surface of the second polycrystalline silicon film.
5. The method according to claim 1, characterized in that, The diameter of the silicon nanoparticles is smaller than the width of the widened grain boundary.
6. The method according to claim 5, characterized in that, The widened grain boundary has a width of 15 nm, and the silicon nanoparticles have a diameter of 10 nm.
7. The method according to claim 1, characterized in that, The thickness of the amorphous silicon layer is 100 nm.
8. The method according to claim 1, characterized in that, The laser used for laser irradiation is a solid-state laser with a wavelength of 532nm.
9. A low-temperature polycrystalline silicon thin film, characterized in that, Prepared by the method according to any one of claims 1 to 8.