Method of filling a trench

Abstract

This application provides a trench filling method. First, a first high-dielectric-constant oxide layer and a second high-dielectric-constant oxide layer are formed sequentially. Then, nitrogen plasma is used to bombard the surface of the epitaxial layer and the surface of the top layer in the deep trench. An isolation oxide layer of a certain thickness is then formed on the top layer using an ALD process. This process is repeated at least ten times until the stacked isolation oxide layer fills all remaining spaces in the deep trench. By bombarding the surface of the epitaxial layer and the surface of the top layer in the deep trench with nitrogen plasma before each cycle of ALD deposition of the isolation oxide layer, this application reduces the active sites of precursor adsorption while nitriding the surface of the top layer, thereby inhibiting the growth of the top layer at the opening of the deep trench and avoiding void defects during deep trench filling.

Description

Technical Field

[0001] This application relates to the field of integrated circuit manufacturing technology, and specifically to a trench filling method. Background Technology

[0002] In deep trench isolation structures, after depositing high-k passivation / isolation dielectric layers (such as Al2O3 and Ta2O5) on the sidewalls and bottom walls of the deep trench using the ALD process, cross-sectioning reveals that the top of the trench contracts inward, resulting in a narrow-bowl-shaped profile. This means the deep trench is narrow at the top and wide in the middle. The main reason for this narrow-bowl shape is that the opening at the top of the deep trench becomes a preferential adsorption site for ALD precursors (such as TMA for Al and TaCl5 for Ta), leading to a slightly higher deposition rate at this location, thus gradually causing the deep trench profile to narrow.

[0003] However, the narrow-mouth morphology of deep trenches is prone to premature sealing of the top opening during the subsequent deposition of the isolation oxide layer, leading to severe void defects inside the deep trenches. Furthermore, in the subsequent alloying process, the deep trench isolation structure with internal void defects is prone to crack defects due to insufficient structural stability and inward stress release. Summary of the Invention

[0004] This application provides a trench filling method that can solve the problems of internal void defects after the deposition of the isolation oxide layer and crack defects after the alloying process in traditional deep trench isolation structures.

[0005] This application provides a method for filling trenches, including: First step: Provide a substrate on which an epitaxial layer is formed, and in which a plurality of mutually spaced deep trenches are formed; Second step: Form a first high dielectric constant oxide layer, which covers the sidewalls and bottom wall of the deep trench; Third step: Form a second high dielectric constant oxide layer, which covers the first high dielectric constant oxide layer. At this time, the cross-section of the remaining space in the deep trench is narrow bottle neck shape. Fourth step: Use nitrogen plasma to bombard the surface of the epitaxial layer and the surface of the top film layer in the deep trench; Fifth step: An isolation oxide layer of a certain thickness is formed using the ALD process, the isolation oxide layer covering the surface of the epitaxial layer and the top film layer in the deep trench; Step 6: Repeat steps 4 and 5 at least ten times until the stacked layers of the isolation oxide layer fill all the remaining space in the deep trench.

[0006] Optionally, in the trench filling method, during each cycle of the fourth step, the RF source power is 2000W~3000W; the nitrogen flow rate is 1500sccm~2000sccm; and the process duration is 0.15h~0.2h.

[0007] Optionally, in the trench filling method, during each cycle of performing the fifth step, an ALD process is used to form the isolation oxide layer of at least 1 angstrom.

[0008] Optionally, in the trench filling method, during each cycle of the fifth step, the participating gases include at least: silicon precursor, oxygen source gas, and argon; the process chamber pressure is 4.3 Torr to 4.7 Torr; and the process temperature is 300°C.

[0009] Optionally, in the trench filling method, an ALD process is used to form a first high dielectric constant oxide layer.

[0010] Optionally, in the trench filling method, the first high dielectric constant oxide layer is made of aluminum oxide.

[0011] Optionally, in the trench filling method, an ALD process is used to form a second high dielectric constant oxide layer.

[0012] Optionally, in the trench filling method, the material of the second high dielectric constant oxide layer is tantalum oxide.

[0013] Optionally, in the trench filling method, after the sixth step, the trench filling method further includes: a seventh step: forming a TEOS layer, the TEOS layer covering the isolation oxide layer.

[0014] Optionally, in the trench filling method, the depth-to-width ratio of the deep trench is 5:1.

[0015] The technical solution of this application has at least the following advantages: In the trench filling method provided in this application, a first high dielectric constant oxide layer and a second high dielectric constant oxide layer are first formed sequentially in the deep trench. Then, nitrogen plasma is used to bombard the surface of the epitaxial layer and the surface of the top layer in the deep trench, and an isolation oxide layer of a certain thickness is formed on the top layer using an ALD process. Then, the steps of nitrogen plasma bombardment + ALD deposition of isolation oxide layer are repeated at least ten times until the stacked multilayer isolation oxide layer fills all the remaining space in the deep trench. This application bombards the surface of the epitaxial layer and the surface of the top layer in the deep trench with nitrogen plasma before each cycle of ALD deposition of the isolation oxide layer. This reduces the active sites of precursor adsorption while nitriding the surface of the top layer, thereby inhibiting the growth of the top layer at the opening of the deep trench and preventing overhang. This results in the growth rate of the isolation oxide layer inside the deep trench being faster than that at the opening of the deep trench, thus preventing premature sealing of the deep trench. In other words, it avoids the formation of voids in the deep trench and prevents the deep trench isolation structure with internal voids from developing cracks due to insufficient structural stability and inward stress release during subsequent alloying processes. This improves the reliability of deep trench filling. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a flowchart of a trench filling method according to an embodiment of the present invention; Figures 2-6 This is a schematic diagram of the semiconductor structure in each process step of filling the trench in an embodiment of the present invention; The reference numerals in the attached figures are explained as follows: 10-Substrate, 20-Epipolar layer, 21-Deep trench, 31-First high dielectric constant oxide layer, 32-Second high dielectric constant oxide layer, 40-Isolation oxide layer. Detailed Implementation

[0018] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0020] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0021] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0022] This application provides a method for filling trenches, referring to... Figure 1 , Figure 1 This is a flowchart of a trench filling method according to an embodiment of this application. The trench filling method includes: First, perform the first step S1: (Refer to...) Figure 2 , Figure 2 This is a schematic diagram of a semiconductor structure after the formation of deep trenches according to an embodiment of this application. A substrate 10 is provided, on which an epitaxial layer 20 is formed, and a plurality of mutually spaced deep trenches 21 are formed in the epitaxial layer 20.

[0023] In this embodiment, the substrate 10 is a silicon substrate, and the epitaxial layer 20 is a silicon epitaxial layer.

[0024] Preferably, the depth-to-width ratio of the deep trench 21 is 5:1.

[0025] Then, proceed to step S2: (Refer to...) Figure 3 , Figure 3 This is a schematic diagram of the semiconductor structure after the formation of the first high dielectric constant oxide layer according to an embodiment of this application. The first high dielectric constant oxide layer 31 is formed, and the first high dielectric constant oxide layer 31 covers the sidewalls and bottom wall of the deep trench 21.

[0026] Preferably, the first high dielectric constant oxide layer 31 is formed using the ALD process.

[0027] Preferably, the first high dielectric constant oxide layer 31 is made of aluminum oxide.

[0028] In this embodiment, the thickness of the first high dielectric constant oxide layer 31 is 15 angstroms to 30 angstroms.

[0029] Next, proceed to step S3: (Refer to...) Figure 4 , Figure 4 This is a schematic diagram of the semiconductor structure after the formation of the second high dielectric constant oxide layer according to an embodiment of this application. The second high dielectric constant oxide layer 32 is formed, and the second high dielectric constant oxide layer 32 covers the first high dielectric constant oxide layer 31. At this time, the cross-section of the remaining space in the deep trench 21 is narrow bottle neck shape.

[0030] In this embodiment, the narrow bottle neck shape is such that the top opening of the deep groove 21 narrows towards the axis of the deep groove, so that the opening size at the top position of the deep groove is smaller than the lateral size at the non-top position of the deep groove.

[0031] In other embodiments, the narrow bottle neck shape can be such that the top opening of the deep groove 21 and the bottom end of the deep groove 21 both shrink towards the axis of the deep groove, so that the opening size at the top position of the deep groove and the lateral dimension at the bottom position of the deep groove are both smaller than the lateral dimension at the middle position of the deep groove.

[0032] Preferably, the second high dielectric constant oxide layer 32 is formed using the ALD process.

[0033] Preferably, the second high dielectric constant oxide layer 32 is made of tantalum oxide.

[0034] In this embodiment, the thickness of the second high dielectric constant oxide layer 32 is 450 angstroms to 550 angstroms.

[0035] In this process, after etching the epitaxial layer 20 to form the deep trench 21, lattice damage layers, silicon dangling bonds, and surface defects will be generated on the sidewalls of the deep trench. These defects will form a large number of interface states (energy levels in the band gap). The first high dielectric constant oxide layer 31 and the second high dielectric constant oxide layer 32 are sequentially formed on the sidewalls of the deep trench 21, which can efficiently passivate the interface states on the sidewalls of the deep trench and suppress carrier recombination and leakage. At the same time, it can provide a reliable transition and protection for the subsequent deep trench filling oxide isolation layer process.

[0036] However, during the formation of the first high dielectric constant oxide layer 31 and the second high dielectric constant oxide layer 32 using the ALD process (e.g., trimethylaluminum TMA for Al2O3 and TaCl5 for Ta2O5), on the one hand, unreacted precursor ligands (e.g., methyl groups of Al and chlorine groups of Ta), physically adsorbed water vapor (H2O), and organic pollutants may remain on the film surface. On the other hand, due to the difference in precursor adsorption sites, the top of the deep trench is a region with dense dangling bonds, which becomes a preferential adsorption site for ALD precursors (e.g., trimethylaluminum TMA of Al and TaCl5 of Ta). This results in a slightly higher film deposition rate at the top of the deep trench than at the inner wall of the deep trench, forming an overhang. That is, the top opening of the deep trench 21 shrinks towards the axis of the deep trench, thus creating a narrow bottle neck shape.

[0037] Further, proceed to step four, S4: (Refer to...) Figure 5 , Figure 5 This is a schematic diagram of a semiconductor structure in which nitrogen plasma is used to bombard the surface of the epitaxial layer and the surface of the top film layer in the deep trench according to an embodiment of this application. Nitrogen plasma is used to bombard the surface of the epitaxial layer 20 and the surface of the top film layer in the deep trench 21.

[0038] During the first bombardment using nitrogen plasma, the surface of the epitaxial layer 20 and the surface of the second high dielectric constant oxide layer 32 in the deep trench 21 are bombarded.

[0039] Preferably, when using nitrogen plasma for the first bombardment, the radio frequency source power is 2000W~3000W; the nitrogen flow rate is 1500sccm~2000sccm; and the process duration is 0.15h~0.2h.

[0040] Next, the fifth step S5 is performed: an isolation oxide layer 40 of a certain thickness is formed using the ALD process, the isolation oxide layer 40 covering the surface of the epitaxial layer 20 and the top film layer in the deep trench 21.

[0041] When the isolation oxide layer 40 of a certain thickness is formed for the first time using the ALD process, the isolation oxide layer 40 covers the surface of the epitaxial layer 20 and the second high dielectric constant oxide layer 32 in the deep trench 21.

[0042] Preferably, during the first execution of the fifth step, the isolation oxide layer 40 of at least 1 angstrom is formed using the ALD process.

[0043] Preferably, during the first execution of the fifth step, the participating gases include at least: silicon precursor, oxygen source gas and argon; the process chamber pressure is 4.3 Torr~4.7 Torr; and the process temperature is 300°C.

[0044] Finally, perform step S6: (Refer to...) Figure 6 , Figure 6 This is a schematic diagram of a semiconductor structure after the stacked multilayer isolation oxide layers of this application have filled all the remaining space in the deep trench. The fourth and fifth steps are executed at least ten times until the stacked multilayer isolation oxide layers have filled all the remaining space in the deep trench.

[0045] In this embodiment, the fourth and fifth steps are executed 20 times in a loop.

[0046] During each cycle of nitrogen plasma bombardment, which is not the first time, the surface of the epitaxial layer 20 and the surface of the isolation oxide layer 40 in the deep trench 21 are bombarded.

[0047] Preferably, during each cycle of the fourth step, the RF source power is 2000W~3000W; the nitrogen flow rate is 1500sccm~2000sccm; and the process duration is 0.15h~0.2h.

[0048] Preferably, during each cycle of the fifth step, the isolation oxide layer of at least 1 angstrom is formed using the ALD process.

[0049] Preferably, during each cycle of the fifth step, the participating gases include at least: silicon precursor, oxygen source gas and argon; the process chamber pressure is 4.3 Torr to 4.7 Torr; and the process temperature is 300°C.

[0050] In this embodiment, the silicon precursor pulse time is 300ms~600ms; the oxygen source gas pulse time is 200ms~400ms; and the argon purging time is 4s~8s.

[0051] Among them, silicon precursors include, but are not limited to, TEOS (tetraethyl orthosilicate); oxygen source gases include, but are not limited to, oxygen.

[0052] Furthermore, after the sixth step S6, the trench filling method may further include: a seventh step S7: forming a TEOS layer (not shown), the TEOS layer covering the isolation oxide layer 40.

[0053] In this application, before each cycle of ALD deposition of the isolation oxide layer, nitrogen plasma is used to bombard the surface of the epitaxial layer and the surface of the top layer in the deep trench. On the one hand, the high-energy electrons, N2⁺ ions, and active N radicals generated by the nitrogen plasma discharge will undergo decomposition / ionization reactions with the residues on the film surface. All products are gaseous and can be directly removed by the vacuum system of the process chamber. At the same time, the gentle bombardment of nitrogen plasma can strip physically adsorbed water vapor and organic contaminants, achieving atomic-level cleaning of the surface of the second high dielectric constant oxide layer 32 and the surface of each isolation oxide layer 40, eliminating electrical and morphological defects caused by residues from the source. On the other hand, each nitrogen plasma bombardment can nitrid the second high dielectric constant oxide layer 32. While reducing the surface area of ​​the surface or each layer of isolation oxide layer by 40, the active sites of precursor adsorption (TMA of Al, TaCl5 of Ta, and TEOS of isolation oxide layer) are reduced, thereby inhibiting the growth of isolation oxide layer at the top opening of the deep trench and avoiding overhang at the top of the deep trench. This makes the growth rate of isolation oxide layer inside the deep trench (inner wall) faster than the growth rate of isolation oxide layer at the top opening of the deep trench, thus avoiding premature sealing of the deep trench. In other words, it avoids the occurrence of void defects in the deep trench, and also avoids the situation where the deep trench isolation structure with internal void defects has insufficient structural stability and stress release inward during subsequent alloying processes, thereby improving the reliability of deep trench filling.

[0054] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A method for filling a trench, characterized in that, include: First step: Provide a substrate on which an epitaxial layer is formed, and in which a plurality of mutually spaced deep trenches are formed; Second step: Form a first high dielectric constant oxide layer, which covers the sidewalls and bottom wall of the deep trench; Third step: Form a second high dielectric constant oxide layer, which covers the first high dielectric constant oxide layer. At this time, the cross-section of the remaining space in the deep trench is narrow bottle neck shape. Fourth step: Use nitrogen plasma to bombard the surface of the epitaxial layer and the surface of the top film layer in the deep trench; Fifth step: An isolation oxide layer of a certain thickness is formed using the ALD process, the isolation oxide layer covering the surface of the epitaxial layer and the top film layer in the deep trench; Step 6: Repeat steps 4 and 5 at least ten times until the stacked layers of the isolation oxide layer fill all the remaining space in the deep trench.

2. The trench filling method according to claim 1, characterized in that, During each cycle of the fourth step, the RF source power is 2000W~3000W; the nitrogen flow rate is 1500sccm~2000sccm; and the process duration is 0.15h~0.2h.

3. The trench filling method according to claim 1, characterized in that, During each cycle of the fifth step, the isolation oxide layer of at least 1 angstrom is formed using the ALD process.

4. The trench filling method according to claim 1, characterized in that, During each cycle of the fifth step, the participating gases include at least: silicon precursor, oxygen source gas, and argon; the process chamber pressure is 4.3 Torr to 4.7 Torr; and the process temperature is 300°C.

5. The trench filling method according to claim 1, characterized in that, The first high dielectric constant oxide layer is formed using the ALD process.

6. The trench filling method according to claim 1, characterized in that, The first high dielectric constant oxide layer is made of aluminum oxide.

7. The trench filling method according to claim 1, characterized in that, A second high dielectric constant oxide layer is formed using the ALD process.

8. The trench filling method according to claim 1, characterized in that, The second high dielectric constant oxide layer is made of tantalum oxide.

9. The trench filling method according to claim 1, characterized in that, Following the sixth step, the trench filling method further includes: Step 7: Form a TEOS layer, which covers the isolation oxide layer.

10. The trench filling method according to claim 1, characterized in that, The depth-to-width ratio of the deep trench is 5:1.

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