Method for improving stability of thin film in semiconductor device

Abstract

The invention discloses a method for improving the stability of a thin film in a semiconductor device. In order to solve the problems of poor quality of a first oxide layer and unstable thickness of a silicon nitride layer in the prior art, the invention provides the following steps: when forming the first oxide layer on a substrate, depositing at least part of the first oxide layer, and then performing annealing treatment based on N2O-containing gas on the first oxide layer; forming a silicon nitride layer on the annealed first oxide layer; and finally, forming a second oxide layer on the silicon nitride layer. The key N2O annealing treatment not only can densify the first oxide layer, reduce defects and improve the quality of the first oxide layer, but also can effectively consume the dichlorosilane precursor remaining on the surface of the wafer, and guarantees the stability of a silicon source during the subsequent growth of the silicon nitride layer, thereby remarkably improving the thickness stability of the silicon nitride layer. The method improves the stability of the whole thin film structure, and facilitates the improvement of the performance and reliability of the device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor technology, and in particular, to a method for improving thin film stability in semiconductor devices. BACKGROUND

[0002] In semiconductor memory technology, non-volatile memory such as flash memory plays a vital role. In a typical flash memory device structure, such as NORD flash memory, a three-layer structure stacked by a bottom oxide layer, a middle silicon nitride layer and a top oxide layer, commonly referred to as oxide-nitride-oxide structure, is usually used as a key dielectric layer in the memory cell, for example, as the inter-gate dielectric layer between the floating gate and the control gate.

[0003] The electrical properties and physical stability of the oxide-nitride-oxide structure are critical to the performance and reliability of the flash memory device. In particular, the quality of the dielectric layer directly affects the retention capability of the stored charge in the floating gate. Defects in the dielectric layer, such as interface states or trap charges, can cause leakage, causing electrons in the floating gate to escape under unintended circumstances, resulting in loss of stored data and affecting the data retention characteristics of the device. In addition, the uniformity and stability of the thickness of the thin films in the structure are also key factors to ensure the consistency of the device performance. For example, the thickness variation of the silicon nitride layer will directly affect the coupling ratio and threshold voltage of the device, and thus affect the read-write performance and reliability of the device.

[0004] In the conventional oxide-nitride-oxide structure preparation process, chemical vapor deposition method is usually used to grow the thin films of each layer. For example, the silicon nitride layer is usually generated by the reaction of dichlorosilane and ammonia at high temperature: 3SiH2Cl2+4NH3->Si3N4+6HCl+6H2. However, in actual production, this reaction may be accompanied by the generation of by-product ammonium chloride: HCl+NH3->NH4Cl, which is easy to be adsorbed on the surface of the device chamber or the wafer, and may cause particle problems. More importantly, the growth of the silicon nitride layer is very sensitive to the stability of the supply of reactants, especially the silicon source dichlorosilane. In continuous process steps, for example, after the growth of the first oxide layer, there may be residual dichlorosilane on the surface of the wafer or in the process chamber. If the amount of these residual dichlorosilane is unstable or uneven at the beginning of the subsequent silicon nitride growth step, it will cause fluctuations in the concentration of dichlorosilane actually involved in the reaction, thereby causing variations in the growth rate of the silicon nitride layer, ultimately leading to instability and non-uniformity of the thickness of the silicon nitride layer, affecting the yield and performance of the device.

[0005] In addition, the quality of the first oxide layer, such as its density and interface characteristics, is also crucial for reducing the leakage path of the floating gate charge. Conventional growth methods corresponding to the first oxide layer, such as simply using a high-temperature oxidation process, can not fully meet the stringent requirements of high-performance memory devices for low defect density and high stability.

[0006] Therefore, how to improve the quality of the first oxide layer and the thickness stability of the silicon nitride layer in the oxide-nitride-oxide structure, especially, to improve the stability of the entire structure, and thus to improve the performance and reliability of semiconductor devices such as NORD flash memory, is a technical problem to be solved in the field of semiconductor manufacturing. SUMMARY

[0007] The present application aims to overcome the problems existing in the preparation process of the oxide-nitride-oxide (ONO) structure of semiconductor devices (such as NORD flash memory) in the prior art. Specifically, the prior art faces at least one of the following challenges:

[0008] Quality problem of the first oxide layer: Conventional growth methods of the first oxide layer (such as simply HTO) can result in a thin film that is not dense enough and has many interface state defects, which can form a leakage path of the storage charge in the floating gate, affecting the data retention characteristics of the device.

[0009] Thickness stability problem of the silicon nitride layer: During the continuous deposition process, the wafer surface can be left with an uncertain amount of silicon source precursor (such as DCS) after the deposition of the first oxide layer. These residues can cause the concentration of the actual silicon source involved in the reaction to be unstable during the subsequent growth of Si3N4, thereby causing the thickness of the Si3N4 layer to be difficult to accurately control, with poor uniformity, affecting the consistency and reliability of the device performance.

[0010] Therefore, an object of the present application is to provide a method for improving the stability of thin films in semiconductor devices, aiming to improve the quality of the first oxide layer and enhance the thickness stability of the subsequent silicon nitride layer.

[0011] To achieve the above object and other related objects, the present application provides a method for improving the stability of thin films in semiconductor devices, comprising:

[0012] Step one, providing a substrate, forming a first oxide layer on the substrate, the method for forming the first oxide layer comprising: depositing at least part of the first oxide layer, and then performing an annealing process based on a N2O-containing gas on the at least part of the first oxide layer;

[0013] Step two, forming a silicon nitride layer on the first oxide layer subjected to the annealing process;

[0014] Step 3: Form a second oxide layer on the silicon nitride layer.

[0015] Preferably, in step one, the deposition of at least a portion of the first oxide layer is performed using a high-temperature oxidation process.

[0016] Preferably, in step one, the annealing treatment based on N2O gas is used to densify the first oxide layer.

[0017] Preferably, prior to step two, the annealing process based on N2O gas is also used to consume the dichlorosilane precursor remaining on the wafer surface after the deposition of the first oxide layer.

[0018] Preferably, the reaction that consumes the dichlorosilane precursor includes: SiH2Cl2 + N2O -> SiO2 + HCl + N2.

[0019] Preferably, in step two, dichlorosilane and ammonia are used as reaction gases to form the silicon nitride layer.

[0020] Preferably, in step two, forming the silicon nitride layer includes performing a heating or cooling process in an oxygen-containing atmosphere.

[0021] Preferably, the oxygen-containing atmosphere is selected from at least one of air, oxygen, or a mixture of oxygen-containing gases.

[0022] Preferably, the semiconductor device is a NORD flash memory device, and the structure is formed between the floating gate and the control gate of the NORD flash memory device.

[0023] Preferably, prior to step one, a floating gate polysilicon layer is formed on the substrate, wherein the first oxide layer is formed on the floating gate polysilicon layer.

[0024] Preferably, before or after forming the floating gate polysilicon layer, the method further includes forming an isolation structure in the substrate.

[0025] As described above, the method for improving thin film stability in semiconductor devices according to the present invention has the following beneficial effects:

[0026] The N2O annealing of the present invention makes the first oxide layer more compact, greatly reducing interface state defects, thereby reducing the escape channels of electrons in the floating gate, which is beneficial to improving the data retention characteristics of the device.

[0027] N2O annealing can effectively consume the DCS precursor remaining on the wafer surface, ensuring a stable and controllable silicon source supply during subsequent silicon nitride growth, thereby significantly improving the stability and uniformity of the silicon nitride thin film thickness.

[0028] In summary, the physical and electrical stability of the entire ONO stack structure is improved. The ONO film prepared using the conditions of this invention (including N2O annealing and oxygen-containing atmosphere heating and cooling) exhibits excellent stability in its online thickness measurement (ONO Film THK), and its thickness fluctuation range (ONO Film Range) can be significantly reduced. This improved stability is of great significance for improving process control, device performance consistency, and the yield and reliability of final products in large-scale integrated circuit manufacturing. Attached Figure Description

[0029] Figure 1 The diagram shown is a schematic representation of the process flow of the present invention.

[0030] Figure 2 The diagram shown illustrates the formation of a floating gate polysilicon layer on a substrate according to the present invention.

[0031] Figure 3 The diagram shows the first oxide layer of the present invention being directly grown on the floating gate polysilicon.

[0032] Figure 4 The diagram shown illustrates the formation of a silicon nitride layer on an annealed first oxide layer according to the present invention.

[0033] Figure 5 The diagram shown illustrates the formation of a second oxide layer on a silicon nitride layer according to the present invention.

[0034] Figure 6 The diagram shows the ONO film prepared according to the present invention, and its online thickness (ONO Film THK) exhibits excellent stability.

[0035] Figure 7 The diagram shown illustrates how the thickness fluctuation range (ONO Film Range) of the ONO film prepared according to the present invention can be significantly reduced. Detailed Implementation

[0036] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0037] This invention provides a method for improving the stability of thin films in semiconductor devices, particularly suitable for improving the stability of thin films containing oxide-nitride-oxide (ONO) structures, wherein the semiconductor device may contain oxide-nitride-oxide structures formed sequentially.

[0038] Please see Figure 1 In one specific embodiment, a method for improving the stability of a thin film in a semiconductor device, the semiconductor device comprising a sequentially formed oxide-nitride-oxide structure, the method comprising:

[0039] Step 1: Forming a first oxide layer 104 on substrate 101; Step 1 includes depositing at least a portion of the first oxide layer 104, and then performing an annealing process based on N2O gas on at least a portion of the first oxide layer 104.

[0040] The N2O annealing treatment is one of the key steps to improve the quality of the first oxide layer 104 and the stability of the subsequent silicon nitride layer 105.

[0041] In some embodiments, the semiconductor device is a NORD flash memory device, and an oxide-nitride-oxide structure is formed between the floating gate and the control gate of the NORD flash memory device. In this application scenario, the ONO structure serves as the inter-gate dielectric layer, and its stability and electrical characteristics (such as leakage current, breakdown voltage, and coupling ratio) directly affect the read / write performance, data retention time, and erase / write lifetime of the NORD flash memory.

[0042] In some embodiments, prior to step one, a floating gate polysilicon layer 103 is further formed on the substrate 101, forming a layer such as... Figure 2 In the structure shown, the first oxide layer 104 is formed on the floating gate polysilicon layer 103. The floating gate is the core unit for storing charge. The first oxide layer 104 is grown directly on the floating gate polysilicon, forming a structure as shown. Figure 3 The structure shown.

[0043] In some embodiments, before or after forming the floating gate polysilicon layer 103, the method further includes forming an isolation structure, such as a shallow trench isolation structure, in the substrate 101. The isolation structure defines the active region of the device, achieving electrical isolation between device cells, and is a fundamental process step in integrated circuit manufacturing. A typical sequence is to form the shallow trench isolation structure, then regenerate the gate oxide layer 102 (if necessary), deposit the floating gate polysilicon layer 103, and then deposit the ONO structure thereon.

[0044] In some embodiments, in step one, the deposition of at least a portion of the first oxide layer 104 employs a high-temperature oxidation process. High-temperature oxidation is a commonly used method for forming high-quality silicon oxide thin films, but using it alone may not fully meet the extreme requirements for film density and interface states. This invention combines high-temperature oxidation deposition with subsequent N₂O annealing to further optimize the characteristics of the first oxide layer 104.

[0045] In some embodiments, in step one, an annealing process using N2O gas is used to densify the first oxide layer 104. By performing N2O annealing after, for example, depositing a partial or full thickness of oxide layer using a high-temperature oxidation process, the tiny voids inside the oxide layer can be effectively filled, potential structural defects can be repaired, and the oxide film structure can be made more compact. A more compact oxide layer has a lower defect density and better insulation properties, and in particular, it can significantly reduce interface state defects at the interface between the first oxide layer 104 and its underlying interface (e.g., the interface with the floating gate polysilicon), thereby greatly reducing the channels through which electrons stored in the floating gate leak through these defects. This is crucial for improving the data retention capability of non-volatile memory devices.

[0046] In some embodiments, prior to step two, the annealing process based on N2O gas is also used to consume the dichlorosilane precursor remaining on the wafer surface after the deposition of the first oxide layer 104. In semiconductor manufacturing processes, cross-contamination or residue of precursors may occur between different process steps. For example, if dichlorosilane (DCS) is introduced in a preceding step or by the environment, or if DCS is introduced in advance for subsequent silicon nitride growth (typically using DCS as the silicon source), an uncertain amount of DCS may be adsorbed or remaining on the wafer surface. This residual DCS can interfere with the precise growth control of the subsequent silicon nitride layer 105. The N2O annealing step in this invention, in addition to densifying the oxide layer, can also chemically react with the residual DCS on the wafer surface, effectively consuming it. This ensures that when entering the formal silicon nitride growth step, the supply of the silicon source (DCS) comes entirely from the controllable gas path of the process equipment, rather than from surface residue, thus laying the foundation for the stable and uniform growth of the subsequent silicon nitride film and solving the problem of silicon nitride thickness fluctuations caused by unstable DCS sources.

[0047] In some embodiments, the reaction consuming the dichlorosilane precursor includes: SiH2Cl2 + N2O -> SiO2 + HCl + N2. This reaction converts residual dichlorosilane into solid silica (which may bind to the surface of the existing oxide layer or be very thin and negligible), gaseous hydrogen chloride, and nitrogen. These products are relatively easy to remove from the process environment or have minimal impact, thereby effectively eliminating DCS residues that affect the stability of subsequent processes.

[0048] Step 2: Form a silicon nitride layer 105 on the annealed first oxide layer 104, forming a structure as shown in the figure. Figure 4 The structure shown; this silicon nitride layer 105 is the intermediate layer in the ONO structure, and its thickness and uniformity have a significant impact on device performance. Since the N2O annealing treatment in step one has already created conditions for stable growth, the thickness of the silicon nitride layer 105 formed in this step will be more stable and controllable.

[0049] In some embodiments, in step two, dichlorosilane and ammonia (NH3) are used as reactant gases to form the silicon nitride layer 105. This is a typical method for growing silicon nitride using low-pressure chemical vapor deposition (LPCVD), with the chemical reaction formula: 3SiH2Cl2 + 4NH3 -> Si3N4 + 6HCl + 6H2 (possibly accompanied by the side reaction 3SiH2Cl2 + 10NH3 -> Si3N4 + 6NH4Cl + 6H2). Precise control of the flow rate, ratio, temperature, and pressure of the DCS and NH3 is crucial to ensuring the quality of the silicon nitride film.

[0050] In some embodiments, step two, forming the silicon nitride layer 105, includes performing a heating or cooling process in an oxygen-containing atmosphere. Compared to conventional heating and cooling in an inert atmosphere such as pure nitrogen, this invention proposes introducing an oxygen-containing atmosphere during the heating or cooling stages before or after silicon nitride deposition (e.g., during wafer loading / unloading in the furnace tube or during process temperature ramping). Doing so can help further remove or oxidize potential residues (such as reaction byproduct NH4Cl), or slightly oxidize the silicon nitride surface, potentially improving interfacial properties with the overlying oxide layer or the overall film stability. See also... Figure 6 and Figure 7 Experimental results show that the introduction of an oxygen-containing atmosphere, combined with the aforementioned N2O annealing, has a positive contribution to the stability of the final ONO film thickness.

[0051] In some embodiments, the oxygen-containing atmosphere is selected from at least one of air, oxygen (O2), or a mixture of oxygen-containing gases. For example, a small amount of pure oxygen can be introduced, or ambient air can be used directly (cleanliness needs to be considered), or oxygen can be mixed with other gases such as nitrogen. The specific choice depends on process requirements and equipment compatibility.

[0052] Step 3: Form a second oxide layer 106 on the silicon nitride layer 105, forming as shown in the figure. Figure 5 The structure shown is an ONO sandwich structure. This layer completes the construction of the ONO sandwich structure and typically serves as the top oxide layer, providing insulation and protection. It can be deposited using methods such as HTO or plasma-enhanced chemical vapor deposition (PECVD).

[0053] In summary, the method proposed in this invention, by introducing an N2O annealing step during the formation of the first oxide layer 104, and optionally combining this with temperature rise and fall in an oxygen-containing atmosphere during the growth of the silicon nitride layer 105, achieves significant technical effects:

[0054] 1. Improve the quality of the first oxide layer 104: N2O annealing makes the first oxide layer 104 more compact, greatly reducing interface state defects, thereby reducing the escape channels of electrons in the floating gate, which is beneficial to improving the data retention characteristics of the device.

[0055] 2. Improve the stability of silicon nitride layer thickness: N2O annealing can effectively consume the DCS precursor remaining on the wafer surface, ensuring a stable and controllable silicon source supply during subsequent silicon nitride growth, thereby significantly improving the stability and uniformity of silicon nitride thin film thickness.

[0056] 3. Improved overall ONO film stability: Combining the above two points, the physical and electrical stability of the entire ONO laminate structure is improved. Please refer to [link / reference]. Figure 6 The ONO film prepared using the conditions of this invention (including N2O annealing and oxygen-containing atmosphere heating and cooling) exhibits excellent stability in its online thickness measurement (ONO Film THK). For example, please refer to... Figure 7 The thickness fluctuation range (ONO Film Range) can be significantly reduced. This improvement in stability is of great significance for process control, device performance consistency, and the improvement of final product yield and reliability in large-scale integrated circuit manufacturing.

[0057] The method of this invention is not only applicable to the ONO structure in NORD Flash, but its core idea, namely, to improve the quality of the lower oxide layer and stabilize the growth conditions of the upper nitride layer through a specific annealing process, can also be applied to other semiconductor devices and manufacturing processes that contain similar oxide-nitride-oxide stacked structures or have high requirements for the stability of dielectric layer thickness.

[0058] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0059] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for improving the stability of thin films in semiconductor devices, characterized in that, At least including: Step 1: Provide a substrate and form a first oxide layer on the substrate. The method for forming the first oxide layer includes: depositing at least a portion of the first oxide layer and then performing an annealing treatment based on N2O gas on the at least a portion of the first oxide layer. Step 2: Form a silicon nitride layer on the first oxide layer after the annealing treatment; Step 3: Form a second oxide layer on the silicon nitride layer.

2. The method for improving thin film stability in semiconductor devices according to claim 1, characterized in that: In step one, at least a portion of the first oxide layer is deposited using a high-temperature oxidation process.

3. The method for improving thin film stability in semiconductor devices according to claim 1 or 2, characterized in that: In step one, the annealing treatment based on N2O gas is used to densify the first oxide layer.

4. The method for improving thin film stability in semiconductor devices according to claim 1, characterized in that: Prior to step two, the annealing process based on N2O gas is also used to consume the dichlorosilane precursor remaining on the wafer surface after the deposition of the first oxide layer.

5. The method for improving thin film stability in semiconductor devices according to claim 4, characterized in that: The reaction that consumes the dichlorosilane precursor includes: SiH2Cl2 + N2O -> SiO2 + HCl + N2.

6. The method for improving thin film stability in semiconductor devices according to claim 1, characterized in that: In step two, dichlorosilane and ammonia are used as reaction gases to form the silicon nitride layer.

7. The method for improving thin film stability in semiconductor devices according to claim 1 or 6, characterized in that: In step two, forming the silicon nitride layer includes performing a heating or cooling process in an oxygen-containing atmosphere.

8. The method for improving thin film stability in semiconductor devices according to claim 7, characterized in that: The oxygen-containing atmosphere is selected from at least one of air, oxygen, or a mixture of oxygen-containing gases.

9. The method for improving thin film stability in semiconductor devices according to claim 1, characterized in that: The semiconductor device is a NORD flash memory device, and the structure is formed between the floating gate and the control gate of the NORD flash memory device.

10. The method for improving thin film stability in semiconductor devices according to claim 9, characterized in that: Prior to step one, a floating gate polysilicon layer is formed on the substrate, wherein the first oxide layer is formed on the floating gate polysilicon layer.

11. The method for improving thin film stability in semiconductor devices according to claim 10, characterized in that: Before or after forming the floating gate polysilicon layer, the method further includes forming an isolation structure in the substrate.

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