Lithography Rework Method for SONOS Memory

Abstract

The present invention provides a photolithography rework method for a SONOS memory, comprising: providing a substrate having a storage area and a non-storage area, sequentially forming a tunneling oxide layer, a nitride layer, and a first photoresist layer to be reworked on the substrate; removing the first photoresist layer; forming a blocking oxide layer on the nitride layer; forming a second photoresist layer on the blocking oxide layer; using the second photoresist layer as a mask to remove the blocking oxide layer and the nitride layer on the non-storage area; removing the second photoresist layer; synchronously removing the remaining blocking oxide layer and the tunneling oxide layer on the non-storage area. Forming the blocking oxide layer on the nitride layer before forming the second photoresist layer solves the problem of poor adhesion between the nitride layer and the second photoresist layer after photolithography rework, and avoids lateral etching of the nitride layer caused by peeling of the photoresist during subsequent etching.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing technology, and particularly to a photolithography rework method for SONOS memories. Background Art

[0002] A SONOS (Silicon-Oxide-Nitride-Oxide-Silicon) memory is a charge trap memory that stores charges using a nitride layer, and has advantages such as a small cell size, a low operating voltage, and compatibility with the COMS process. Since the advent of SONOS memories, they have continuously promoted the development of memories towards miniaturization, large capacity, and low cost.

[0003] A SONOS memory has a storage area and a non-storage area. During the preparation process of a SONOS memory, a tunneling oxide layer and a nitride layer are generally formed on a substrate first, and the tunneling oxide layer and the nitride layer on the non-storage area are removed through processes such as photolithography and etching, and then subsequent film layers are formed. Figures 1 to 3 For a structural schematic diagram corresponding to the corresponding steps of a SONOS memory preparation method, as Figure 1 shown, the substrate has a storage area a and a non-storage area b, and a stacked tunneling oxide layer 202, a nitride layer 203, and a first photoresist layer 204 are sequentially formed on the substrate 200. During the exposure and development processes of the first photoresist 204, due to factors such as machine errors, the critical dimension (CD) of the first photoresist layer 204 or the overlay accuracy with the machine may not meet the process requirements. At this time, it is necessary to strip the first photoresist layer 204 for rework, and then reapply the photoresist and perform photolithography.

[0004] As Figure 2 and Figure 3As shown, the first photoresist layer 204 is removed, and then a second photoresist layer 205 is reformed on the nitride layer 203 in the storage area a, and the nitride layer 203 and the tunneling oxide layer 202 on the non-storage area b are etched away using the second photoresist layer 205 as a mask. Specifically, the first photoresist layer 204 is removed using a dry ashing process, and then the substrate 200 is further cleaned using a chemical solution such as sulfuric acid to remove the residual first photoresist layer 204 on the surface of the nitride layer 203 and the polymers generated during the dry ashing process. Since sulfuric acid has strong water absorption and corrosiveness, the sulfuric acid solution will change the properties of the surface of the nitride layer 203 during the cleaning process. In addition, although the substrate 200 will be rinsed with clean water and other steps after sulfuric acid cleaning, there will still inevitably be some sulfuric acid solution remaining on the nitride layer 203, resulting in poor adhesion between the nitride layer 203 and the second photoresist layer 205. In order to ensure that the nitride layer 203 and the tunneling oxide layer 202 on the non-storage area b are etched clean, a wet etching process is generally used, and the etching time is relatively long. During the etching process, the second photoresist layer 205 is immersed in the wet etching solution for a long time, and the adhesion between the nitride layer 203 and the second photoresist layer 205 becomes further poor, resulting in lateral etching of the nitride layer 203 in the edge area of the storage area a by the wet etching solution, affecting the performance of the SONOS memory. Moreover, as the semiconductor device size continues to shrink, the memory failure probability caused by lateral etching further increases, seriously affecting the product yield. Summary of the Invention

[0005] The purpose of the present invention is to provide a photolithography rework method for a SONOS memory to solve the problem of lateral etching caused by poor adhesion between the photoresist and the nitride layer during the existing photolithography rework process.

[0006] To achieve the above purpose, the present invention provides a photolithography rework method for a SONOS memory, including:

[0007] Providing a substrate having a storage area and a non-storage area, and sequentially forming a tunneling oxide layer, a nitride layer, and a first photoresist layer to be reworked on the substrate;

[0008] Removing the first photoresist layer;

[0009] Forming a blocking oxide layer on the nitride layer;

[0010] Forming a second photoresist layer on the blocking oxide layer;

[0011] Using the second photoresist layer as a mask to remove the blocking oxide layer and the nitride layer on the non-storage area;

[0012] Removing the second photoresist layer;

[0013] Simultaneously remove the remaining blocking oxide layer and the tunneling oxide layer on the non-storage area.

[0014] Optionally, the step of removing the first photoresist layer includes:

[0015] Perform a dry ashing process on the first photoresist layer to remove the first photoresist layer;

[0016] Clean the substrate with sulfuric acid.

[0017] Optionally, the step of removing the blocking oxide layer and the nitride layer on the non-storage area using the second photoresist layer as a mask includes:

[0018] Use a dry etching process to remove the blocking oxide layer on the non-storage area;

[0019] Use a first wet etching process to remove the nitride layer on the non-storage area.

[0020] Optionally, the etchant used in the first wet etching process is phosphoric acid.

[0021] Optionally, the thickness of the blocking oxide layer is 0.5 to 1.5 times the thickness of the tunneling oxide layer.

[0022] Optionally, use a second wet etching process to simultaneously remove the remaining blocking oxide layer and the tunneling oxide layer on the non-storage area.

[0023] Optionally, the etchant used in the second wet etching process is hydrofluoric acid.

[0024] Optionally, the step of removing the second photoresist layer includes:

[0025] Perform a dry ashing process on the second photoresist layer to remove the second photoresist layer;

[0026] Clean the substrate with sulfuric acid.

[0027] Optionally, after simultaneously removing the remaining blocking oxide layer and the tunneling oxide layer on the non-storage area, it further includes:

[0028] Form a gate oxide layer on the substrate, and the gate oxide layer covers the nitride layer and the substrate of the non-storage area.

[0029] Optionally, the upper surface height of the substrate in the storage area is lower than the upper surface height of the substrate in the non-storage area.

[0030] An embodiment of the present invention provides a photolithography rework method for a SONOS memory, including: providing a substrate having a storage area and a non-storage area, and sequentially forming a tunneling oxide layer, a nitride layer, and a first photoresist layer to be reworked on the substrate; removing the first photoresist layer; forming a blocking oxide layer on the nitride layer; forming a second photoresist layer on the blocking oxide layer; using the second photoresist layer as a mask to remove the blocking oxide layer and the nitride layer on the non-storage area; removing the second photoresist layer; synchronously removing the remaining blocking oxide layer and the tunneling oxide layer on the non-storage area. By forming the blocking oxide layer on the nitride layer during the photolithography rework process, it is ensured that there is good adhesion between the blocking oxide layer and the second photoresist layer and the nitride layer, solving the problem of poor adhesion between the nitride layer and the second photoresist layer after removing the first photoresist layer, effectively avoiding the problem of peeling of the second photoresist layer at the edge of the storage area and lateral etching of the nitride layer caused by reduced adhesion during the subsequent etching process, and ensuring the performance and product yield of the SONOS memory. Description of the Drawings

[0031] Figures 1 to 3 It is a schematic structural diagram corresponding to the corresponding steps of a photolithography rework method for a SONOS memory;

[0032] Figure 4 It is a flowchart of a photolithography rework method for a SONOS memory provided by an embodiment of the present invention;

[0033] Figures 5 to 13 It is a schematic structural diagram corresponding to the corresponding steps of a photolithography rework method for a SONOS memory provided by an embodiment of the invention;

[0034] Among them, the reference numerals are:

[0035] A, a - storage area; B, b - non-storage area;

[0036] 100, 200 - substrate; 101, 201 - shallow trench isolation structure; 102, 202 - tunneling oxide layer; 103, 203 - nitride layer; 104, 204 - first photoresist layer; 105 - blocking oxide layer; 106 - second photoresist layer; 107 - gate oxide layer. Detailed Embodiments

[0037] The following will describe the specific embodiments of the present invention in more detail with reference to the schematic diagrams. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the drawings are all in a very simplified form and use non-precise scales, only for conveniently and clearly assisting in explaining the purpose of the embodiments of the present invention.

[0038] In the following text, the terms "first", "second", etc. are used to distinguish between similar elements and are not necessarily used to describe a specific order or chronological order. It is understood that, where appropriate, these terms so used may be interchanged. Similarly, if the methods described herein include a series of steps, and the steps presented herein are not necessarily the only order in which these steps can be performed, and some of the described steps may be omitted and / or some other steps not described herein may be added to the method.

[0039] Figure 4 The flowchart of a lithography rework method for a SONOS memory provided in this embodiment is as Figure 4 shown. The lithography rework method for the SONOS memory includes:

[0040] Step S1: Provide a substrate having a storage area and a non-storage area. A tunneling oxide layer, a nitride layer, and a first photoresist layer to be reworked are sequentially formed on the substrate;

[0041] Step S2: Remove the first photoresist layer;

[0042] Step S3: Form a blocking oxide layer on the nitride layer;

[0043] Step S4: Form a second photoresist layer on the blocking oxide layer;

[0044] Step S5: Using the second photoresist layer as a mask, remove the blocking oxide layer and the nitride layer on the non-storage area;

[0045] Step S6: Remove the second photoresist layer;

[0046] Step S7: Synchronously remove the remaining blocking oxide layer and the tunneling oxide layer on the non-storage area.

[0047] Figures 5 to 13 The schematic structural diagram corresponding to the corresponding steps of a lithography rework method for a SONOS memory provided in this embodiment. Next, it will be described in detail in combination with Figures 5 to 13 the lithography rework method for the SONOS memory.

[0048] As Figure 5As shown, a substrate 100 is provided. The substrate 100 has a storage area A and a non-storage area B. The non-storage area B includes a selection area and a peripheral logic area. There is a shallow trench isolation structure 101 in the substrate 100 between the selection area and the peripheral logic area. On the substrate 100, a stacked tunneling oxide layer 102, a nitride layer 103, and a first photoresist layer 104 to be reworked are formed in sequence. The tunneling oxide layer 102 covers the substrate 100, the nitride layer 103 covers the tunneling oxide layer 102, and the first photoresist layer 104 covers the nitride layer 103 on the storage area A. During the processes such as exposure and development of the first photoresist layer 104, due to factors such as machine errors, problems such as critical dimension errors or misalignment accuracy with the machine not meeting the process requirements occur. Therefore, the first photoresist layer 104 needs to be stripped for photolithography rework.

[0049] Among them, the upper surface height of the substrate 100 in the storage area A is lower than the upper surface height of the substrate 100 in the non-storage area B to reduce the height difference between the nitride layer 103 and the substrate 100 in the non-storage area B.

[0050] As Figure 6 shown, the first photoresist layer 104 is removed. Specifically, first, a dry ashing process is performed on the first photoresist layer 104 to remove the first photoresist layer 104. However, some polymers that are difficult to remove will be generated during the dry ashing process of the first photoresist layer 104. The polymers adhere to the surface of the nitride layer 103. Therefore, after the dry ashing process, the substrate 100 needs to be further cleaned. Generally, a strongly corrosive acidic solution (such as sulfuric acid solution) is selected as the cleaning agent to remove the remaining first photoresist layer 104 and the polymers to ensure the surface cleanliness of the nitride layer 103.

[0051] After removing the first photoresist layer 104, the substrate 100 will also be cleaned with clean water to remove the remaining sulfuric acid solution. However, due to the strong dehydrating property and low volatility of sulfuric acid, some sulfuric acid will still remain on the surface of the nitride layer 103 after clean water cleaning, affecting the adhesion between the nitride layer 103 and the subsequent film layers. And during the process of using sulfuric acid solution to clean the polymers on the surface of the nitride layer 103, the nitride layer 103 reacts slowly with the sulfuric acid solution, forming a film layer with different properties from the nitride layer 103 on the surface of the nitride layer 103, further affecting the adhesion between the nitride layer 103 and the photoresist.

[0052] As Figures 7 to 8As shown, a barrier oxide layer 105 is formed on the nitride layer 103. The barrier oxide layer 105 covers the nitride layer 103. Among them, the barrier oxide layer 105 is formed by a chemical vapor deposition process, so that there is good adhesion between the barrier oxide layer 105 and the nitride layer 103. The thickness of the barrier oxide layer 105 is 0.5 to 1.5 times the thickness of the tunneling oxide layer 102.

[0053] Further, a second photoresist layer 106 is spin-coated on the barrier oxide layer 105, and the second photoresist layer 106 is subjected to an exposure and development process to form a patterned second photoresist layer 106 that covers the barrier oxide layer 105 on the storage area A. There is good adhesion between the second photoresist layer 106 and the barrier oxide layer 105.

[0054] As Figures 9 to 10 shown, using the second photoresist layer 106 as a mask, the barrier oxide layer 105 and the nitride layer 103 on the non-storage area B are etched away in sequence until the tunneling oxide layer 102 is exposed.

[0055] Specifically, the barrier oxide layer 105 is etched by a dry etching process, and then the nitride layer 103 is etched by the first wet etching process. Since the dry etching process has the characteristic of anisotropy, it is possible to avoid lateral etching of the barrier oxide layer 105 in the storage area A during the etching process while removing the barrier oxide layer 105 on the non-storage area B. However, during the process of etching the barrier oxide layer 105 using the dry etching process, the nitride layer 103 on part of the non-storage area B will also be affected by the dry etching process, resulting in uneven thickness of the nitride layer 103. If the dry etching process is continued to etch the nitride layer 103 at this time, it may cause damage to the substrate 100. Therefore, in this embodiment, the first wet process is used to etch the nitride layer 103; the etching agent used in the first wet process is phosphoric acid. Since phosphoric acid is a weak acid and phosphoric acid reacts with the nitride layer 103 but does not react with the tunneling oxide layer 102, using phosphoric acid to etch the nitride layer 103 can prevent the etching agent from eroding the tunneling oxide layer 102 under the nitride layer 103 while ensuring that the nitride layer 103 is completely removed, thereby preventing damage to the substrate 100.

[0056] As Figure 11As shown, except for the second photoresist layer 106, a dry ashing process is first performed on the second photoresist layer 106, and then the remaining second photoresist layer 106 and the polymer generated during the dry ashing process are cleaned using a sulfuric acid solution. Since the barrier oxide layer 105 is below the second photoresist layer 106, the sulfuric acid cleaning process will not damage the nitride layer 103, which better protects the nitride layer 103.

[0057] As Figure 12 shown, the remaining barrier oxide layer 105 and the tunneling oxide layer 102 on the non-storage area B are synchronously removed. Since the thickness difference between the barrier oxide layer 105 and the tunneling oxide layer 102 is small, the barrier oxide layer 105 and the tunneling oxide layer 102 can be synchronously removed within substantially the same etching time, and the two film layers are etched away in one step to reduce the process steps. At the same time, the shorter etching time can also reduce the erosion of the nitride layer 103 under the barrier oxide layer 105 during the etching process.

[0058] In addition, a second wet etching process is used to remove the barrier oxide layer 105 and the tunneling oxide layer 102, and the etching agent used in the second wet etching process is hydrofluoric acid. Hydrofluoric acid has good selectivity for silicon oxide and silicon nitride. During the process of removing the barrier oxide layer 105 and the tunneling oxide layer 102, the damage to the nitride layer 103 is minimized to ensure the performance of the SONOS memory.

[0059] As Figure 13 shown, a gate oxide layer 107 is formed on the substrate 100. The gate oxide layer 107 covers the nitride layer 103 and the substrate 100 of the non-storage area B. The tunneling oxide layer 102, the nitride layer 103, and the gate oxide layer 107 on the storage area A constitute an ONO layer.

[0060] In summary, the embodiment of the present invention provides a photolithography rework method for a SONOS memory, including: providing a substrate 100, where the substrate 100 has a storage area A and a non-storage area B, and a tunneling oxide layer 102, a nitride layer 103, and a first photoresist layer 104 to be reworked are sequentially formed on the substrate 100; removing the first photoresist layer 104; forming a barrier oxide layer 105 on the nitride layer 103; forming a second photoresist layer 106 on the barrier oxide layer 105; using the second photoresist layer as a mask to remove the barrier oxide layer 105 and the nitride layer 103 on the non-storage area B; removing the second photoresist layer 106; synchronously removing the remaining barrier oxide layer 105 and the tunneling oxide layer 102 on the non-storage area B. By forming the barrier oxide layer 105 on the nitride layer 103 during the photolithography rework process, it is ensured that there is good adhesion between the barrier oxide layer 105 and the second photoresist layer 104 and the nitride layer 103, solving the problem that the adhesion between the nitride layer 103 and the second photoresist layer 106 becomes poor after removing the first photoresist layer 104, effectively avoiding the problem of peeling of the second photoresist layer 106 at the edge of the storage area A and lateral etching of the nitride layer 103 caused by reduced adhesion during the subsequent etching process, and ensuring the performance and product yield of the SONOS memory.

[0061] The above is only a preferred embodiment of the present invention and does not impose any limitation on the present invention. Any person skilled in the art, without departing from the technical solution of the present invention, makes any form of equivalent substitution or modification and other changes to the technical solution and technical content disclosed by the present invention, which are all within the content of the technical solution of the present invention and still fall within the protection scope of the present invention.

Claims

1. A lithography rework method for a SONOS memory, characterized in that, Including: Providing a substrate, the substrate having a storage area and a non-storage area, and sequentially forming a tunneling oxide layer, a nitride layer, and a first photoresist layer to be reworked on the substrate; Removing the first photoresist layer; Forming a blocking oxide layer on the nitride layer; Forming a second photoresist layer on the blocking oxide layer; Using the second photoresist layer as a mask to remove the blocking oxide layer and the nitride layer on the non-storage area; Removing the second photoresist layer; Simultaneously removing the remaining blocking oxide layer and the tunneling oxide layer on the non-storage area.

2. The lithography rework method of the SONOS memory according to claim 1, wherein The step of removing the first photoresist layer includes: Performing a dry ashing process on the first photoresist layer to remove the first photoresist layer; Cleaning the substrate with sulfuric acid.

3. The lithography rework method of the SONOS memory according to claim 1, characterized in that, The step of using the second photoresist layer as a mask to remove the blocking oxide layer and the nitride layer on the non-storage area includes: Using a dry etching process to remove the blocking oxide layer on the non-storage area; Using a first wet etching process to remove the nitride layer on the non-storage area.

4. The lithography rework method of the SONOS memory according to claim 3, characterized in that, The etching agent used in the first wet etching process is phosphoric acid.

5. The lithography rework method of the SONOS memory according to claim 1, characterized in that, The thickness of the blocking oxide layer is 0.5 to 1.5 times the thickness of the tunneling oxide layer.

6. The lithography rework method of the SONOS memory according to claim 1 or 5, characterized in that Using a second wet etching process to simultaneously remove the remaining blocking oxide layer and the tunneling oxide layer on the non-storage area.

7. The lithography rework method of the SONOS memory according to claim 6, characterized in that, The etching agent used in the second wet etching process is hydrofluoric acid.

8. The lithography rework method of the SONOS memory according to claim 1, characterized in that, The step of removing the second photoresist layer includes: Performing a dry ashing process on the second photoresist layer to remove the second photoresist layer; Cleaning the substrate with sulfuric acid.

9. The lithography rework method of the SONOS memory according to claim 1, characterized in that After simultaneously removing the remaining blocking oxide layer and the tunneling oxide layer on the non-storage area, further including: Forming a gate oxide layer on the substrate, the gate oxide layer covering the nitride layer and the substrate of the non-storage area.

10. The photolithography rework method of the SONOS memory according to claim 1, characterized in that, The upper surface of the substrate in the storage area is lower than the upper surface of the substrate in the non-storage area.

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