Method for filling deep groove

Abstract

The invention discloses a method for filling a deep trench, which comprises the following process steps of: etching on a semiconductor substrate to form the deep trench, the deep trench being an isolation trench with a depth-to-width ratio greater than 20; forming a liner layer in the deep trench, wherein the liner layer isolates a deep trench filler from the semiconductor substrate; filling the deep groove filler for the first time, wherein the filling thickness is that the groove is not sealed; carrying out an etching process with the same property, and etching the filler in the groove to enable the section of the groove to be in a V shape; and filling the deep groove filler for the second time, and filling the deep groove with the deep groove filler.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing, and particularly to a method for filling deep trenches. Background Art

[0002] DTI (Deep Trench Isolation) is a trench with a large aspect ratio. The insulating isolation layer formed by the deep trench is used to isolate sensitive analog circuits or high-voltage devices, which can improve the performance and stability of integrated circuits. Compared with the conventional shallow structure isolated by holes, the DTI process can provide better insulation effect, low power consumption, high integration and higher speed.

[0003] For deep trenches with a depth greater than 20um, the conventional method is that after the DTI trench etching is completed, a pad oxide layer is first grown on the inner wall of the trench to isolate the subsequently filled polysilicon from the silicon substrate. After the pad oxide layer is grown, the aspect ratio of the original deep trench will be further enlarged. Because the conventional method is to directly deposit polysilicon in one step to fill the deep trench, this will cause the polysilicon to close at the top of the trench in advance, and voids will be formed in the middle and lower parts of the trench, resulting in the trench not being filled with polysilicon and causing serious filling gaps. As Figure 1 shown, it is a deep trench filled by the existing process. After filling the polysilicon, obvious voids can be seen in the internal cross-section of the trench under a microscope. For example, for a deep trench filling that requires filling polysilicon with a thickness of 12000Å, after actual filling, a filling gap with a height of 8800Å and a width of 1300Å may be formed in the trench, which will greatly affect the device performance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for filling deep trenches to solve the problem that deep trenches cannot be completely filled.

[0005] To solve the above problem, the present invention provides a method for filling DTI trenches, including the following process steps: Etching is performed on a semiconductor substrate to form a deep trench, and the deep trench is an isolation trench with an aspect ratio greater than 20; A liner layer is formed in the deep trench, and the liner layer isolates the deep trench filler from the semiconductor substrate; Perform the first filling of the deep trench filler, and the filling thickness is such that the trench does not close; Perform an isotropic etching process to etch the filler in the trench so that the trench cross-section presents a V shape; Perform the second filling of the deep trench filler to fill the deep trench completely.

[0006] Further, the semiconductor substrate is a silicon substrate, or a silicon-germanium substrate, a gallium arsenide substrate, a gallium nitride substrate, or a silicon carbide substrate.

[0007] Further, the cushion layer is a silicon oxide layer; the thickness of the cushion layer only needs to meet the isolation performance under the current device operating voltage.

[0008] Further, for the first filling of the deep trench filler, the filling thickness is 1000 - 3000 Å, covering the cushion layer and leaving a certain opening in the deep trench.

[0009] Further, the isotropic etching process is a dry etching process, and the etching amount is 1000 - 4000 Å; after etching, the sidewall morphology of the trench is improved to make the cross-section of the deep trench V-shaped, which can increase the opening degree of the deep trench.

[0010] Further, for the second filling of the deep trench filler, the filling thickness is 12000 Å to fill the remaining space of the deep trench.

[0011] Further, the deep trench filler contains polysilicon.

[0012] In the filling method of the DTI trench of the present invention, after the formation of the deep trench liner oxide layer, the filling of the deep trench is carried out step by step. The first filling is at a lower thickness, and then an additional isotropic etching process is added to modify the sidewall morphology of the deep trench into a V-shape, which can expand the opening of the deep trench. Then, the second deposition step of filling the deep trench is carried out. Since the additional isotropic etching process expands the opening width of the deep trench, the filling effect of the deep trench is more ideal, and the occurrence of defects such as filling voids caused by direct one-time filling of the deep trench is reduced. Description of the Drawings

[0013] Figure 1 is a practical micrograph of the existing deep trench filling process method where the opening of the deep trench closes prematurely during filling, resulting in incomplete filling inside the deep trench and the formation of voids.

[0014] Figure 2 is a schematic diagram of the substrate etching step of the present invention to form a deep trench.

[0015] Figure 3 is a schematic diagram of the liner oxide layer deposition step of the present invention.

[0016] Figure 4 is a schematic diagram of the first polysilicon deposition step of the present invention with a thickness of 1000 - 3000 Å.

[0017] Figure 5 is a schematic diagram of the isotropic etching step of the present invention to form a V-shaped opening.

[0018] Figure 6 It is a schematic diagram of filling the deep trench with a thickness of 12,000 Å for the second time in the process steps of the present invention.

[0019] Figure 7 It is a cross-sectional physical diagram of the deep trench after the filling process steps of the present invention are completed.

[0020] Figure 8 It is a process flow diagram of the present invention. Specific Embodiments

[0021] The following provides specific embodiments of the present invention in conjunction with the accompanying drawings, and clearly and completely describes the technical solutions in the present invention. However, the present invention is not limited to the following embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. According to the following description and the claims, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise ratios, only for the purpose of facilitating and clearly assisting in explaining the purpose of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0022] The present invention can be implemented in different forms and should not be construed as limited to the embodiments presented herein. On the contrary, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. In the drawings, for clarity, the dimensions and relative dimensions of layers and regions may be exaggerated, and the same reference numerals throughout the drawings indicate the same elements. In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application 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 construed as a limitation of the present application. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0023] The process of the present invention mainly solves the problem of filling deep trenches, where the trench opening is sealed in advance, resulting in filling voids inside the trench.

[0024] As Figure 2 shown, first, deep trench etching is performed on the semiconductor substrate to form deep trenches that meet the design requirements of the aspect ratio. For example, in this embodiment, the depth of the deep trench is 35 μm and the width is 0.7 μm.

[0025] A buffer layer, such as a silicon oxide layer, is formed in the deep trench to electrically isolate the filler in the trench from the substrate, or to improve the adhesion between different materials, etc. In the present invention, the thickness of the buffer layer needs to meet the isolation requirements. After the buffer layer is deposited, as Figure 3 shown. It should be noted that only the film layer state in the deep trench area is shown in the attached drawings of the present invention, and the film layer state outside the deep trench area, including the surface of the substrate, is not shown.

[0026] The first deposition filling of the trench filler is carried out, such as depositing polysilicon. The thickness of the first deposition is 1000 - 3000 Å, which covers the surface of the buffer layer, but there is still a large remaining space in the deep trench. As Figure 4 shown. It should be noted that the film layer inside the deep trench in this schematic diagram is relatively uniform. In the actual process, since the upper part of the trench is more likely to come into contact with the reaction gas, the film layer in the upper part of the deep trench is thicker than that in the lower part of the trench. This is also the reason why the trench opening is likely to be sealed in advance in the traditional process of one-time filling.

[0027] An isotropic etching process is carried out to modify the morphology inside the deep trench. For example, the polysilicon deposited on the inner wall of the trench and even the buffer layer are etched to a certain extent by a dry etching process, as Figure 5 shown. The isotropic dry etching forms a V-shaped cross-section inside the deep trench. In this etching step, the trench opening is enlarged, which is beneficial to the subsequent filling process.

[0028] The isotropic etching amount can be adjusted according to the film thickness formed in the previous step. Generally, the etching amount is 1000 - 4000 Å. Enough V-shaped openings are formed in the deep trench without excessive loss of the buffer layer at the trench opening.

[0029] The second polysilicon filling is carried out. The remaining space of the deep trench is completely filled with polysilicon deposited with a thickness of 12000 Å at one time, and the filling process of the deep trench is completed. As Figure 6 shown. Since the trench opening is enlarged, the reaction gas can more easily enter the inside of the deep trench for reaction during the deposition filling, and the enlarged trench opening can compensate for the problem of premature sealing caused by too fast deposition at the opening during deposition, which is more beneficial to the filling of the deep trench. Therefore, the second filling can more completely fill the deep trench and ensure the filling effect inside the deep trench.

[0030] Figure 7 shown is the cross-section of the deep trench filled by the process of the present invention. Compared with the filling effect of the existing process shown in Figure 1 , the difference is obvious. The inside of the trench is basically filled, and no obvious gaps are found.

[0031] For the filling of deep trenches in the present invention, after growing the liner layer, the deep trenches are filled in two steps. First, a filler with a thickness of 1000 - 3000 Å is grown without filling the trenches completely. An additional step of isotropic dry etching is added to improve the cross-sectional morphology of the deep trenches, forming a V-shaped cross-section in the deep trenches. Then, the second filling is carried out to fill the deep trenches completely, solving the defect problem of serious gaps caused by the difficulty in filling the deep trenches.

[0032] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for filling a deep trench, characterized in that: It includes the following process steps: Etching is performed on a semiconductor substrate to form deep trenches, and the deep trenches are isolation trenches with an aspect ratio greater than 20; A liner layer is formed in the deep trenches, and the liner layer isolates the deep trench filler from the semiconductor substrate; The first filling of the deep trench filler is carried out, and the filling thickness is such that the trench is not sealed; An isotropic etching process is performed to etch the filler in the trench so that the trench profile presents a V shape; The second filling of the deep trench filler is carried out to fill the deep trench completely; 2. The filling method of the deep trench according to claim 1, wherein: The semiconductor substrate is a silicon substrate, or a silicon-germanium substrate, a gallium arsenide substrate, a gallium nitride substrate, or a silicon carbide substrate; 3. The filling method of the deep trench according to claim 1, wherein: The liner layer is a silicon oxide layer; the thickness of the liner layer only needs to meet the isolation performance under the working voltage of the current device; 4. The filling method of the deep trench according to claim 1, characterized in that: For the first filling of the deep trench filler, the filling thickness is 1000 - 3000 Å, covering the liner layer and keeping a certain opening of the deep trench; 5. The filling method of the deep trench according to claim 1, characterized in that: The isotropic etching process is a dry etching process, and the etching amount is 1000 - 4000 Å; after the etching is completed, the sidewall morphology of the trench is improved so that the deep trench profile presents a V shape, which can increase the opening degree of the deep trench; 6. The filling method of the deep trench according to claim 1, wherein: For the second filling of the deep trench filler, the filling thickness is 12000 Å to fill the remaining space of the deep trench completely; 7. The filling method of the deep trench according to any one of claims 1 to 6, characterized in that: The deep trench filler contains polysilicon.

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