Methods for improving the chamfering of table structures

Abstract

This invention provides a method for improving the chamfering of mesa structures. A substrate is provided, an ONO layer is formed on the substrate, and a deep trench is formed on the ONO layer and the substrate below it. A third oxide layer is formed on the surface of the deep trench using thermal oxidation. The protrusion of the nitride layer relative to the mesa structure is controlled to a first length using etch-back. A fourth oxide layer and a first polysilicon layer are sequentially formed in the deep trench, and the first polysilicon layer is etched back to the desired height. A fifth oxide layer is formed on the first polysilicon layer, and a photoresist layer is formed on the fifth oxide layer, with the photoresist layer protruding a second length relative to the first polysilicon layer. Using the photoresist layer and the nitride layer as etch stop layers, a shallow trench is formed between the mesa structure and the deep trench using etching, removing the photoresist layer and the remaining ONO layer. A sixth oxide layer and a second polysilicon layer are sequentially formed in the shallow trench, and the second polysilicon layer is etched back to the desired height. This invention can improve the chamfering problem of mesa structures.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for improving the chamfering of mesa structures. Background Technology

[0002] Fully depleted SGT (trench gate) is a common design for medium-voltage SGTs, which are typically semi-depleted. Industry-leading full-depletion (Full SGT) solutions can reduce Rsp (parasitic resistance) by more than 30% and have lower conduction losses.

[0003] Full SGT employs deep trench technology and IPO (inter-gate oxide) dry etching. During the process flow, the MESA (mesa structure) is prone to beveled, affecting the subsequent source region implantation junction depth and easily causing short-channel leakage.

[0004] To solve the above problems, a new method for improving the chamfering of the countertop structure is needed. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for improving the beveling of the mezzanine structure, so as to solve the problem that the mezzanine structure is easily beveled in the prior art, which affects the subsequent source region injection junction depth and easily causes short-channel leakage.

[0006] To achieve the above and other related objectives, the present invention provides a method for improving the chamfering of a countertop structure, comprising:

[0007] Step 1: Provide a substrate and form an ONO layer on the substrate. The ONO layer consists of a first oxide layer, a nitride layer, and a second oxide layer stacked sequentially from bottom to top. Deep trenches are formed on the ONO layer and the substrate below it. The substrate between the deep trenches has a mesa structure.

[0008] Step 2: A third oxide layer is formed on the surface of the deep trench using thermal oxidation, and the protrusion of the nitride layer relative to the mesa structure is controlled to a first length using back etching.

[0009] Step 3: Sequentially form a fourth oxide layer and a first polysilicon layer in the deep trench, and then etch the first polysilicon layer back to the required height;

[0010] Step 4: Form a fifth oxide layer on the first polysilicon layer, and form a photoresist layer on the fifth oxide layer, wherein the protrusion of the photoresist layer relative to the first polysilicon layer is a second length;

[0011] Step 5: Using the photoresist layer and the nitride layer as etching barrier layers, a shallow trench is formed between the mesa structure and the deep trench using an etching method, and the photoresist layer and the remaining ONO layer are removed.

[0012] Step 6: Sequentially form a sixth oxide layer and a second polysilicon layer in the shallow trench, and then etch the second polysilicon layer back to the desired height.

[0013] Preferably, the deep trench is formed in step one using photolithography and etching methods.

[0014] Preferably, the back etching in step two is wet etching.

[0015] Preferably, the first length in step two is 500 to 800 angstroms.

[0016] Preferably, the fourth oxide layer in step three is silicate glass free of infiltrated impurities.

[0017] Preferably, the etching method in step three is dry etching.

[0018] Preferably, the etching method in step five is dry etching.

[0019] Preferably, in step five, the photoresist layer is removed using an ashing process and a wet cleaning method.

[0020] Preferably, in step five, the remaining ONO layer is removed using a wet etching method.

[0021] Preferably, the etching method in step six is ​​dry etching.

[0022] As described above, the method for improving the chamfering of the countertop structure according to the present invention has the following beneficial effects:

[0023] This invention can improve the problem of chamfering in countertop structures. Attached Figure Description

[0024] Figure 1 The image shown is a schematic diagram of an electron microscope image of the morphology of a mesa structure in the prior art.

[0025] Figure 2 The diagram shown is a schematic representation of the process flow of the present invention.

[0026] Figure 3 The diagram shown illustrates the formation of deep trenches according to the present invention.

[0027] Figure 4 The diagram shown illustrates the formation of the third oxide layer according to the present invention.

[0028] Figure 5The diagram shown is a schematic diagram of the etch-back nitride layer of the present invention.

[0029] Figure 6 The diagram shown is a schematic diagram of the first polysilicon layer being etched back according to the present invention.

[0030] Figure 7 The diagram shown illustrates the formation of shallow trenches according to the present invention.

[0031] Figure 8 The diagram shown illustrates the formation of the sixth oxide layer and the second polycrystalline silicon layer according to the present invention.

[0032] Figure 9 The diagram shown is a schematic diagram of the second polysilicon layer being etched back according to the present invention.

[0033] Figure 10 The image shown is a schematic electron microscope photograph of the topography of the mesa structure of the present invention. Detailed Implementation

[0034] 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.

[0035] Please see Figure 2 The present invention provides a method for improving the chamfering of a countertop structure, comprising:

[0036] Step 1: Provide a substrate 101 and form an ONO layer on the substrate 101. The ONO layer consists of a first oxide layer 102, a nitride layer 103, and a second oxide layer 104 stacked sequentially from bottom to top. Deep trenches are formed on the ONO layer and the substrate 101 below it. The substrate 101 between the deep trenches has a mesa structure.

[0037] First, the material of the first oxide layer is usually silicon dioxide, and the material of the nitride layer 103 is silicon nitride. The thickness of the nitride layer 103 needs to be sufficient to prevent it from being completely etched in the subsequent dry etching. For example, the thickness of the first oxide layer 102 is 500 angstroms, the thickness of the nitride layer 103 is 2600 angstroms, and the thickness of the second oxide layer 104 is 5000 angstroms.

[0038] In some embodiments, deep trenches are formed in step one using photolithography and etching methods.

[0039] Step 2: Form a third oxide layer 105 on the surface of the deep trench using thermal oxidation, forming a layer such as... Figure 4The structure shown utilizes an etch-back method to control the protrusion of the nitride layer 103 relative to the mesa structure to a first length h1, forming a structure as shown. Figure 5 The structure shown retains the nitride layer 103 as a protective layer for the mesa structure during subsequent etching, preventing the formation of structures like... Figure 1 The chamfered corner shown reduces the amount of protrusion retained, thus minimizing etching on the trench sidewalls.

[0040] In some embodiments, the back etching in step two is wet etching.

[0041] In some embodiments, the first length in step two is 500 to 800 angstroms.

[0042] Step 3: Sequentially form the fourth oxide layer 106 and the first polysilicon layer 107 in the deep trench, and then etch the first polysilicon layer 107 back to the required height to form a structure as shown in the figure. Figure 6 In the structure shown, the upper surface of the first polysilicon layer 107 may be located near the upper surface of the mesa structure, for example, slightly below the upper surface of the mesa structure.

[0043] In some embodiments, the fourth oxide layer 106 in step three is silicate glass free of infiltrating impurities.

[0044] In some embodiments, the etching method in step three is dry etching.

[0045] Step 4: A fifth oxide layer 108 is formed on the first polysilicon layer 107, and a photoresist layer 109 is formed on the fifth oxide layer 108. The protrusion of the photoresist layer 109 relative to the first polysilicon layer 107 is the second length h2. In the subsequent etching, a portion of the fourth oxide layer 106 can be retained as the IPO (inter-gate oxide layer) between the first and second polysilicon layers.

[0046] Step 5: Using photoresist layer 109 and nitride layer 103 as etching barrier layers, shallow trenches are formed between the mesa structure and the deep trench using etching methods, forming a structure like... Figure 7 The structure shown is modified by removing the photoresist layer 109 and the remaining ONO layer; please refer to [link / reference]. Figure 10 The image shows an electron microscope image of the shallow trench formed by the process of the present invention, which shows that the chamfering of the platform structure is improved.

[0047] In some embodiments, the etching method in step five is dry etching.

[0048] In some embodiments, step five involves removing the photoresist layer 109 using an ashing process and a wet cleaning method.

[0049] In some embodiments, the remaining ONO layer is removed in step five using a wet etching method.

[0050] Step Six: Sequentially form the sixth oxide layer and the second polysilicon layer 110 in the shallow trench, forming as shown in the figure. Figure 8 The structure shown is formed by etching the second polysilicon layer 110 back to the desired height, forming a structure as shown. Figure 9 In the structure shown, the upper surface of the second polysilicon layer 110 may be located near the upper surface of the mesa structure, for example, slightly below the upper surface of the mesa structure.

[0051] In some embodiments, the etching method in step six is ​​dry etching.

[0052] 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.

[0053] In summary, this invention can improve the problem of chamfering in countertop structures. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0054] 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 chamfering of a countertop structure, characterized in that, At least including: Step 1: Provide a substrate and form an ONO layer on the substrate. The ONO layer consists of a first oxide layer, a nitride layer, and a second oxide layer stacked sequentially from bottom to top. Deep trenches are formed on the ONO layer and the substrate below it. The substrate between the deep trenches has a mesa structure. Step 2: A third oxide layer is formed on the surface of the deep trench using thermal oxidation, and the protrusion of the nitride layer relative to the mesa structure is controlled to a first length using back etching. Step 3: Sequentially form a fourth oxide layer and a first polysilicon layer in the deep trench, and then etch the first polysilicon layer back to the required height; Step 4: Form a fifth oxide layer on the first polysilicon layer, and form a photoresist layer on the fifth oxide layer, wherein the protrusion of the photoresist layer relative to the first polysilicon layer is a second length; Step 5: Using the photoresist layer and the nitride layer as etching barrier layers, a shallow trench is formed between the mesa structure and the deep trench using an etching method, and the photoresist layer and the remaining ONO layer are removed. Step 6: Sequentially form a sixth oxide layer and a second polysilicon layer in the shallow trench, and then etch the second polysilicon layer back to the desired height.

2. The method for improving the chamfering of the countertop structure according to claim 1, characterized in that: In step one, the deep trench is formed using photolithography and etching methods.

3. The method for improving the chamfering of the countertop structure according to claim 1, characterized in that: The etching process described in step two is wet etching.

4. The method for improving the chamfering of the countertop structure according to claim 1, characterized in that: The first length in step two is 500 to 800 angstroms.

5. The method for improving the chamfering of the countertop structure according to claim 1, characterized in that: The fourth oxide layer in step three is silicate glass without infiltrated impurities.

6. The method for improving the chamfering of the countertop structure according to claim 1, characterized in that: The etching method described in step three is dry etching.

7. The method for improving the chamfering of the countertop structure according to claim 1, characterized in that: The etching method described in step five is dry etching.

8. The method for improving the chamfering of the countertop structure according to claim 1, characterized in that: In step five, the photoresist layer is removed using an ashing process and a wet cleaning method.

9. The method for improving the chamfering of the countertop structure according to claim 1, characterized in that: In step five, the remaining ONO layer is removed using a wet etching method.

10. The method for improving the chamfering of the countertop structure according to claim 1, characterized in that: The etching method described in step six is ​​dry etching.

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