Method for improving chamfering of table-board structure

Abstract

The invention provides a method for improving a chamfer angle of a mesa structure, which comprises the following steps of: providing a substrate, forming an ONO layer on the substrate, and forming a deep trench on the ONO layer and the substrate below the ONO layer; forming a third oxide layer on the surface of the deep trench by using a thermal oxidation method, and controlling the protruding amount of the nitride layer relative to the mesa structure to be a first length by using a back etching method; a fourth oxide layer and a first polycrystalline silicon layer are sequentially formed in the deep trench, and the first polycrystalline silicon layer is etched back to the required height; a fifth oxide layer is formed on the first polycrystalline silicon layer, a photoresist layer is formed on the fifth oxide layer, and the protruding amount of the photoresist layer relative to the first polycrystalline silicon layer is a second length; taking the photoresist layer and the nitride layer as etching barrier layers, forming a shallow trench between the mesa structure and the deep trench by using an etching method, and removing the photoresist layer and the residual ONO layer; and sequentially forming a sixth oxide layer and a second polycrystalline silicon layer in the shallow trench, and back-etching the second polycrystalline silicon layer to a required height. According to the invention, the chamfering problem of the table-board structure can be improved.

Description

Technical Field

[0001] The invention relates to the field of semiconductor technology, and in particular to a method for improving chamfering of a mesa structure. Background Art

[0002] Fully depleted SGT (trench gate), medium voltage SGT is usually a semi-depleted design. The industry-leading level adopts the full depletion (Full SGT) solution, which can reduce Rsp (parasitic resistance) by more than 30% and has low conduction loss.

[0003] Full SGT uses deep trench process and IPO (inter-gate oxide layer) dry etching process. In the process flow, MESA (mesa structure) is easily chamfered, which affects the depth of subsequent source injection junction and is prone to short channel leakage.

[0004] In order to solve the above problems, it is necessary to propose a new method for improving the chamfering of the table structure. Summary of the invention

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

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

[0007] Step 1, providing a substrate, forming an ONO layer on the substrate, wherein the ONO layer consists of a first oxide layer, a nitride layer, and a second oxide layer stacked in sequence from bottom to top, forming deep trenches on the ONO layer and the substrate below it, and the substrate between the deep trenches is a mesa structure;

[0008] Step 2: forming a third oxide layer on the surface of the deep trench by a thermal oxidation method, and controlling the protrusion of the nitride layer relative to the mesa structure to a first length by an etch-back method;

[0009] Step 3, sequentially forming a fourth oxide layer and a first polysilicon layer in the deep trench, and etching back the first polysilicon layer to a desired height;

[0010] Step 4: forming a fifth oxide layer on the first polysilicon layer, and forming a photoresist layer on the fifth oxide layer, wherein the protrusion amount 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, forming a shallow groove between the mesa structure and the deep groove by an etching method, and removing the photoresist layer and the remaining ONO layer;

[0012] Step six: sequentially forming a sixth oxide layer and a second polysilicon layer in the shallow trench, and etching back the second polysilicon layer to a desired height.

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

[0014] Preferably, the back etching in step 2 is wet etching.

[0015] Preferably, the first length in step 2 is 500 to 800 angstroms.

[0016] Preferably, the fourth oxide layer in step three is silicate glass without infiltration of impurities.

[0017] Preferably, the back 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 by using an ashing process and a wet cleaning method.

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

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

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

[0023] The present invention can improve the chamfering problem of the table structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The schematic diagram of the electron microscope photo of the mesa structure (mesa) morphology of the prior art is shown;

[0025] Figure 2 Shown is a schematic diagram of the process flow of the present invention;

[0026] Figure 3 It is a schematic diagram of forming a deep trench according to the present invention;

[0027] Figure 4 It is a schematic diagram showing the formation of a third oxide layer according to the present invention;

[0028] Figure 5It is a schematic diagram of etching back the nitride layer of the present invention;

[0029] Figure 6 It is a schematic diagram of etching back the first polysilicon layer according to the present invention;

[0030] Figure 7 Shown is a schematic diagram of forming a shallow trench according to the present invention;

[0031] Figure 8 It is a schematic diagram showing the formation of the sixth oxide layer and the second polysilicon layer of the present invention;

[0032] Fig. 9 It is a schematic diagram of etching back the second polysilicon layer according to the present invention;

[0033] Fig.10 Shown is a schematic diagram of an electron microscope photograph of the mesa structure morphology of the present invention. DETAILED DESCRIPTION

[0034] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0035] See also Figure 2 The present invention provides a method for improving the chamfering of a mesa structure, comprising:

[0036] Step 1, providing a substrate 101, forming an ONO layer on the substrate 101, the ONO layer consisting of a first oxide layer 102, a nitride layer 103, and a second oxide layer 104 stacked in sequence from bottom to top, forming deep trenches on the ONO layer and the substrate 101 below it, and the substrate 101 between the deep trenches is a mesa structure;

[0037] The material of the first oxide layer 102 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, in step 1, a deep trench is formed by photolithography and etching.

[0039] Step 2: Form a third oxide layer 105 on the surface of the deep trench by thermal oxidation. Figure 4The structure shown in FIG. 1 is formed by controlling the protrusion of the nitride layer 103 relative to the mesa structure to a first length h1 by using a back etching method. Figure 5 The structure shown in FIG. 1 is a structure in which the retained nitride layer 103 is used as a protective layer for the mesa structure in the subsequent etching process to avoid the formation of the mesa structure due to etching. Figure 1 The chamfer shown, the remaining protrusion can reduce the etching of the trench sidewall;

[0040] In some embodiments, the etch-back in step 2 is wet etching.

[0041] In some embodiments, the first length in step 2 is 500 to 800 angstroms.

[0042] Step 3: sequentially form a fourth oxide layer 106 and a first polysilicon layer 107 in the deep trench, and etch back the first polysilicon layer 107 to a desired height to form a 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 lower than the upper surface of the mesa structure;

[0043] In some embodiments, the fourth oxide layer 106 in step 3 is silicate glass without any impurities.

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

[0045] Step 4: forming a fifth oxide layer 108 on the first polysilicon layer 107, and forming a photoresist layer 109 on the fifth oxide layer 108, wherein the protrusion of the photoresist layer 109 relative to the first polysilicon layer 107 is a second length h2, and a portion of the fourth oxide layer 106 may be retained as an IPO (inter-gate oxide layer) between the first and second polysilicon layers in subsequent etching;

[0046] Step 5: Using the photoresist layer 109 and the nitride layer 103 as etching barrier layers, a shallow groove is formed between the mesa structure and the deep groove by etching. Figure 7 The structure shown in FIG. 1 is shown with the photoresist layer 109 and the remaining ONO layer removed; see FIG. Fig.10 , which shows an electron microscope photograph of a shallow groove formed by the process of the present invention, and it can be seen that the chamfer of the mesa structure is improved;

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

[0048] In some embodiments, in step five, the photoresist layer 109 is removed by using an ashing process and a wet cleaning method.

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

[0050] Step 6: sequentially forming a sixth oxide layer and a second polysilicon layer 110 in the shallow trench to form a Figure 8 The structure shown in FIG. 1 is further structured by etching back the second polysilicon layer 110 to a desired height to form a Fig. 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 lower than the upper surface of the mesa structure.

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

[0052] It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0053] In summary, the present invention can improve the chamfering problem of the table structure. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0054] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may 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 a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for improving the chamfering of a table structure, characterized in that: At least: Step 1, providing a substrate, forming an ONO layer on the substrate, wherein the ONO layer consists of a first oxide layer, a nitride layer, and a second oxide layer stacked in sequence from bottom to top, forming deep trenches on the ONO layer and the substrate below it, and the substrate between the deep trenches is a mesa structure; Step 2: forming a third oxide layer on the surface of the deep trench by a thermal oxidation method, and controlling the protrusion of the nitride layer relative to the mesa structure to a first length by an etch-back method; Step 3, sequentially forming a fourth oxide layer and a first polysilicon layer in the deep trench, and etching back the first polysilicon layer to a desired height; Step 4: forming a fifth oxide layer on the first polysilicon layer, and forming a photoresist layer on the fifth oxide layer, wherein the protrusion amount 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, forming a shallow groove between the mesa structure and the deep groove by an etching method, and removing the photoresist layer and the remaining ONO layer; Step six: sequentially forming a sixth oxide layer and a second polysilicon layer in the shallow trench, and etching back the second polysilicon layer to a desired height.

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

3. The method for improving the chamfering of a table structure according to claim 1, characterized in that: The back etching in step 2 is wet etching.

4. The method for improving the chamfering of a table structure according to claim 1, characterized in that: The first length in step 2 is 500 to 800 angstroms.

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

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

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

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

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

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

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