Method for improving uniformity of NAND block word line and selection tube

Abstract

The invention discloses a method for improving the uniformity of an NAND block word line and a selection tube, and relates to the technical field of semiconductor manufacturing, the method comprises the following steps: manufacturing a word line sacrificial layer through photoetching and etching, manufacturing a word line through a side wall process, manufacturing a selection tube grid through photoetching and etching, and requiring that the edge of the selection tube grid just falls in the word line. The numbers of word lines covered by the selection tubes are unequal; removing a sacrificial layer of the word line, performing subsequent etching on a grid electrode of the selection tube, defining the edge of the overlapped part of the selection tube and the word line by the edge of the word line in order to ensure the accuracy and the consistency of the edge, and determining the distance between the selection tube and the word line by controlling the pattern of an exposure layer of the word line according to the design and the corresponding process flow; and finally, the edge word lines are designed to be covered by the selection tubes, the non-uniformity of the edge word lines is transferred to the internal word lines, and the overall uniformity is optimized.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor manufacturing, in particular to a method for improving the uniformity of NAND block word lines and selection tubes. Background Art

[0002] In the NAND block, there are word lines and select tubes, both of which are gates of the series channel of the NAND block. However, due to the different channel sizes, the two are independently defined and manufactured using two photolithography layers. Therefore, the distance between the word line and the select tube at the edge of the block will be affected by the alignment of the two photolithography layers and there will be uniformity problems. In addition, in the current general manufacturing method, the word line adjacent to the select tube is at the edge of the word line photolithography layer pattern, which will cause the word line pattern morphology adjacent to the select tube, and the key dimensions of the line and line spacing to have uniformity problems.

[0003] From the attached Figure 2 It can be seen that, since the select tube and word line are defined independently by two lithography levels in the existing process, there will be an alignment deviation problem between the two lithography levels. If an advanced lithography machine is used, this deviation may be several to 10 nanometers. In more advanced NAND processes, the distance between word lines and the distance between word lines and select tubes is about 20 nanometers or even smaller, so the alignment deviation between the two lithography levels has a more obvious impact on the distance between word lines and the distance between word lines and select tubes.

[0004] From the attached Figure 1 To the attached Figure 3 It can be seen that in the existing process, the word line near the selector is an edge pattern in the word line manufacturing process. In the advanced NAND process, due to various process capability deviations, the word line at the edge or the distance between the word lines is prone to poor uniformity of key dimensions, and the word line morphology is also prone to be inconsistent with the morphology of other word lines. Summary of the invention

[0005] The object of the present invention is to provide a method for improving the uniformity of NAND block word lines and selection tubes to solve the problems raised in the prior art.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The method for improving the uniformity of NAND block word lines and selection tubes comprises the following steps:

[0008] Step 1: In the NAND block, there are word lines and select tubes, both of which are gates of the series channel of the NAND block. The pattern of the select tube gate is transferred to the substrate material using photolithography technology, and then the pattern is converted into a three-dimensional structure through etching technology;

[0009] Step 2: During the layout design stage, the edge of the selector gate is set on the geometric center line of the word line, and the gate and the word line are made symmetrical during the processing;

[0010] Step 3: Cover different numbers of word lines on the select tube gate according to the design requirements of NAND;

[0011] Step 4: remove the word line sacrificial layer. The sacrificial layer is a temporary layer used to protect the word line in subsequent processing steps. After removing the sacrificial layer, the word line can be independent of other structures.

[0012] Step 5: Perform subsequent etching on the gate of the selection tube. After the etching is completed, the pattern of the gate of the selection tube is transferred to the substrate material, and the head and tail word lines are cut off;

[0013] Step 6: After the etching and word line cutting steps are completed, the final pattern of the selection tube is defined by the selection tube exposure pattern at the edge away from the word line direction;

[0014] Step 7, for the portion where the selection tube overlaps with the word line, in the direction close to the word line, the final pattern of the selection tube is defined by the edge of the word line that overlaps with the exposure pattern of the selection tube;

[0015] Step 8: According to the results of Step 7 and Step 8, the distance between the final pattern of the selection tube and the word line is defined by the word line exposure layer. The distance between the selection tube and the word line is controlled by adjusting the size and position of the exposure layer.

[0016] Step 9: After the exposure layer position and size are adjusted, the edge word lines are covered with selection tubes to transfer the non-uniformity of the edge word lines to the internal word lines.

[0017] The method of transferring the pattern of the selector gate to the substrate material by using the photolithography technology and then converting the pattern into a three-dimensional structure by using the etching technology includes the following steps:

[0018] Step 1.1: Making an insulating layer: Select a base material, clean and treat the surface, and make a layer of insulating material on the base material as an insulating layer for the gate of the selection tube;

[0019] Step 1.2: Manufacturing photolithography mask: First, use electronic design automation tools to design the pattern of the selection tube gate and generate a photolithography mask pattern, and then manufacture the photolithography mask according to the designed pattern;

[0020] Step 1.3: Photolithography step: Place the manufactured photolithography mask on the substrate material, and use light sources of different wavelengths for photolithography according to the photolithography requirements to cause chemical changes in the photoresist in the area corresponding to the mask pattern;

[0021] Step 1.4: Development step: Place the exposed substrate material into a developer to dissolve the exposed portion of the photoresist to form a pattern of the selector gate;

[0022] Step 1.5: Etching step: Place the developed substrate material into an etching solution, and use the etching solution to erode the pattern area on the substrate material according to the design requirements, and transfer the pattern defined by the photoresist to the substrate material.

[0023] The method of setting the edge of the gate of the selection tube on the geometric center line of the word line and making the gate symmetrical with the word line during the processing includes the following steps:

[0024] Step 2.1: Design word line pattern and select transistor gate pattern: First, design the word line pattern in the electronic design automation software so that the geometric center line of the word line is clear and measurable; then, design the select transistor gate pattern in the EDA software so that its edge is aligned with the geometric center line of the word line pattern;

[0025] Step 2.2: Photolithography alignment: Use the high-precision alignment system of the photolithography machine to align the substrate material with the photolithography mask on the photolithography machine to accurately align the word line with the gate pattern of the selection tube.

[0026] The method of covering different numbers of word lines on the gate of the selection tube comprises the following steps:

[0027] Step 3.1: Determine the coverage strategy: Select the design of the gate pattern as described in step 2.1 so that it can cover different numbers of word lines as needed;

[0028] Step 3.2: Implement word line coverage: The coverage method is: form a first word line on the selection tube gate, and the first word line covers a partial area of ​​the selection tube gate, and the partial area refers to setting the coverage ratio and width according to design requirements, rather than full coverage; form a second word line on the first word line, the second word line covers a partial area of ​​the first word line, and the width of the second word line is different from that of the first word line; form a third word line on the second word line, the third word line covers a partial area of ​​the second word line, and the width of the third word line is different from that of the second word line; repeat the above steps until the required number of word lines are formed on the selection tube gate.

[0029] The method of removing the word line sacrificial layer to make the word line independent of other structures comprises the following steps:

[0030] Step 4.1: Sacrificial layer design: After completing the coverage of the selector gate in the previous step, design and form a sacrificial layer above the word line according to the design requirements;

[0031] Step 4.2: Formation of sacrificial layer and protective layer: After the above steps of designing the sacrificial layer are completed, a sacrificial layer is formed on the word line using chemical vapor deposition and physical vapor deposition methods according to the design results; after the sacrificial layer is formed, a protective layer needs to be formed on the sacrificial layer;

[0032] Step 4.3: Removing the sacrificial layer: using a plasma etching process to remove the sacrificial layer; the steps of the removal method are as follows: firstly, determining the etching rate and the position of the sacrificial layer, and monitoring the etching rate and depth while performing the etching process;

[0033] The subsequent etching of the selection tube gate, transferring the pattern of the selection tube gate to the substrate material after the etching is completed, and cutting the head and tail word lines include the following steps:

[0034] Step 5.1: Transferring the pattern of the selection tube grid: On the basis of the selection tube grid already formed on the substrate material, the pattern of the selection tube grid is prepared by using electron beam lithography technology, and then the selection tube grid is etched by plasma etching technology to transfer the pattern to the substrate material to form the required three-dimensional structure;

[0035] Step 5.2: Word line cutting: According to the design requirements, first determine the specific location of the word line cutting, then set the cutting path and mode in the cutting area, adjust the cutting parameters, and finally use plasma cutting technology to perform the cutting operation.

[0036] After the etching and word line cutting steps are completed, the final pattern of the selection tube is defined by the selection tube exposure pattern at the edge away from the word line direction, including the following contents:

[0037] Step 6.1: Exposure pattern preparation: First, according to the design requirements of the selection tube, use the CAD tool to design the outer edge pattern of the selection tube that meets the design requirements, then evenly coat the photoresist on the substrate material, and use the drying program to control the thickness and quality of the photoresist;

[0038] Step 6.2: Exposure and development: After the exposure pattern is prepared, the photoresist-coated substrate material is exposed using a photolithography machine, the exposure dose and resolution are controlled, and the outer edge pattern of the selected tube is matched with the design pattern; after exposure, the substrate material is placed in a developer for development operation;

[0039] Step 6.3: Etching the edge of the selector: After the exposure and development steps are completed, according to the design requirements, the edge of the selector gate away from the word line direction needs to be etched; and the shape and size of the selector gate are controlled by adjusting the etching rate.

[0040] The method of defining the final pattern of the selection tube by the edge of the word line overlapping the selection tube exposure pattern in the direction close to the word line includes the following steps:

[0041] Step 7.1: Photolithography process: Place the mask with the exposure pattern of the selector tube on the wafer for exposure processing, then put the exposed wafer into the developer to form the pattern of the selector tube, and finally use the etching solution to etch away the part not protected by the photoresist to form the structure of the selector tube on the wafer;

[0042] Step 7.2: Alignment and overlap check: In the overlapping area of ​​the select tube and the word line, and in the direction close to the word line, the pattern of the select tube matches the edge of the word line. The high-precision alignment system of the lithography machine is required to confirm the alignment of the exposure pattern of the select tube with the word line, and check the overlap between the two.

[0043] The final pattern of the selection tube and the distance between the word lines are defined by the word line exposure layer and include the following steps:

[0044] Step 8.1: Adjust the size of the exposure layer pattern: According to the design requirements, use electron beam lithography technology to control the size of the exposure layer pattern according to the design parameters, then use computer-aided design software to accurately design the exposure layer pattern, and use the high resolution capability of the lithography machine to transfer the design pattern to the exposure layer; calculate the size of the exposure layer pattern using the following formula:

[0045] L=D+σ L

[0046] Where D represents the distance between the selection tube and the word line according to the design requirements, L represents the size of the exposure layer pattern, σ L Represents the margin reserved to take into account process deviations;

[0047] Taking into account the optical diffraction effect in the photolithography process, the size of the exposure layer pattern can be corrected by the following formula:

[0048] L′=L+λsin(t)

[0049] Wherein, L′ represents the corrected exposure layer pattern size, λ represents the photolithography wavelength, and t represents the diffraction angle;

[0050] Step 8.2: Adjust the exposure layer pattern position: After the exposure layer pattern size design is completed, the exposure layer position is fine-tuned in the horizontal and vertical directions, and then the alignment system of the lithography machine is used to control the spacing between the two through mechanical positioning and alignment; and phase shift exposure technology is used at the same time to confirm the position and spacing of the pattern;

[0051] For fine-tuning the exposure layer position, the new exposure layer position can be calculated using the following formula:

[0052] X′=X+σ X

[0053] Where X is the original exposure layer position, X′ is the new exposure layer position, σ X For fine-tuning amount;

[0054] Taking into account the accuracy and error of the lithography machine alignment system, the following formula can be used to correct the position of the exposure layer:

[0055] X″=X′+ε

[0056] Where X″ represents the position of the corrected exposure layer, and ε represents the error of the alignment system of the lithography machine;

[0057] However, phase-shifted exposure can be achieved by adjusting the exposure dose and phase, and the position of the pattern after exposure can be calculated by the following formula:

[0058] X″′=X″+I·cos(ψ)

[0059] Where X″′ represents the position of the pattern after exposure, I represents the exposure dose, and ψ represents the phase shift.

[0060] The method of covering the edge word line with the selection tube and transferring the non-uniformity of the edge word line to the internal word line comprises the following steps:

[0061] Step 9.1: Edge word line design: After the exposure layer size and position adjustment are completed and the distance between the final pattern of the tube and the word line is confirmed, the layout and shape of the edge word line are designed according to the design requirements;

[0062] Step 9.2: Selector tube layout: After the edge word line design is completed, the size and shape of the selector tube are planned according to the design requirements of the edge word line, and the position and layout of the selector tube are further arranged;

[0063] Step 9.3: Non-uniformity transfer mechanism: After the edge word line design and selection tube layout are completed according to the above steps, after the edge word line is covered by the selection tube, the edge word line and the selection tube are analyzed for non-uniformity using an electrical test method to confirm the existing non-uniformity characteristics and distribution;

[0064] Step 9.4: Transfer to internal word lines: Based on the analysis result of the non-uniformity mechanism, the non-uniformity is transferred by establishing a physical connection between the edge word lines and the internal word lines.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] 1. Improve the uniformity of the word lines at the edge of the NAND block: Through specific technical means, the differences between the edge word lines can be reduced, so that they are more evenly distributed in the NAND block. This method can effectively improve the uniformity of the word lines at the edge of the NAND block.

[0067] 2. Improve the uniformity of the distance between the word lines and the select tubes at the edge of the NAND block: By precisely controlling the positions of the word lines and the select tubes, the deviation of the distance can be reduced, thereby improving the performance and consistency of the entire NAND block. This method can not only improve the uniformity of the word lines, but also improve the uniformity of the distance between the word lines and the select tubes at the edge of the NAND block.

[0068] 3. Improve the performance and reliability of NAND flash memory: The uniformity of word lines and selection tubes is crucial to the performance and reliability of NAND flash memory. Through the application of this method, the non-uniformity between word lines and selection tubes can be reduced, the failure risk of storage cells can be reduced, and the accuracy and stability of data reading and writing can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 A schematic diagram of the structure of making word lines and word line sacrificial layers in a method for improving the uniformity of NAND block word lines and select tubes of the present invention;

[0070] Figure 2 A schematic diagram of the structure of manufacturing a selection tube gate in a method for improving the uniformity of NAND block word lines and selection tubes of the present invention;

[0071] Figure 3 A schematic diagram of the structure of subsequent tube gate etching and head and tail word line cutting in a method for improving the uniformity of NAND block word lines and selection tubes of the present invention;

[0072] Figure 4 A schematic diagram of the structure of improving the manufacturing of word lines and word line sacrificial layers in a method for improving the uniformity of NAND block word lines and selection tubes of the present invention;

[0073] Figure 5 A schematic diagram of the structure of improving the manufacturing of the gate of the selection tube in a method for improving the uniformity of the NAND block word line and the selection tube of the present invention;

[0074] Figure 6 A schematic diagram of a structure in which a word line sacrificial layer is removed in a method for improving the uniformity of a NAND block word line and a selection tube according to the present invention;

[0075] Figure 7 The present invention is a structural schematic diagram of improving subsequent tube gate etching and head and tail word line cutting in a method for improving the uniformity of NAND block word lines and selection tubes. DETAILED DESCRIPTION

[0076] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0077] Example: Figure 1-Figure 7 As shown, the present invention provides a technical solution, a method for improving the uniformity of NAND block word lines and selection tubes, comprising the following steps:

[0078] Step 1: In the NAND block, there are word lines and select tubes, both of which are gates of the series channel of the NAND block. The pattern of the select tube gate is transferred to the substrate material using photolithography technology, and then the pattern is converted into a three-dimensional structure through etching technology;

[0079] Step 2: During the layout design stage, the edge of the selector gate is set on the geometric center line of the word line, and the gate and the word line are made symmetrical during the processing;

[0080] Step 3: Cover different numbers of word lines on the select tube gate according to the design requirements of NAND;

[0081] Step 4: remove the word line sacrificial layer. The sacrificial layer is a temporary layer used to protect the word line in subsequent processing steps. After removing the sacrificial layer, the word line can be independent of other structures.

[0082] Step 5: Perform subsequent etching on the gate of the selection tube. After the etching is completed, the pattern of the gate of the selection tube is transferred to the substrate material, and the head and tail word lines are cut off;

[0083] Step 6: After the etching and word line cutting steps are completed, the final pattern of the selection tube is defined by the selection tube exposure pattern at the edge away from the word line direction;

[0084] Step 7, for the portion where the selection tube overlaps with the word line, in the direction close to the word line, the final pattern of the selection tube is defined by the edge of the word line that overlaps with the exposure pattern of the selection tube;

[0085] Step 8: According to the results of Step 7 and Step 8, the distance between the final pattern of the selection tube and the word line is defined by the word line exposure layer. The distance between the selection tube and the word line is controlled by adjusting the size and position of the exposure layer.

[0086] Step 9: After the exposure layer position and size are adjusted, the edge word lines are covered with selection tubes to transfer the non-uniformity of the edge word lines to the internal word lines.

[0087] The method of transferring the pattern of the selector gate to the substrate material by using the photolithography technology and then converting the pattern into a three-dimensional structure by using the etching technology includes the following steps:

[0088] Step 1.1: Making an insulating layer: Select a base material, clean and treat the surface, and make a layer of insulating material on the base material as an insulating layer for the gate of the selection tube;

[0089] Step 1.2: Manufacturing photolithography mask: First, use electronic design automation tools to design the pattern of the selection tube gate and generate a photolithography mask pattern, and then manufacture the photolithography mask according to the designed pattern;

[0090] Step 1.3: Photolithography step: Place the manufactured photolithography mask on the substrate material, and use light sources of different wavelengths for photolithography according to the photolithography requirements to cause chemical changes in the photoresist in the area corresponding to the mask pattern;

[0091] Step 1.4: Development step: Place the exposed substrate material into a developer to dissolve the exposed portion of the photoresist to form a pattern of the selector gate;

[0092] Step 1.5: Etching step: Place the developed substrate material into an etching solution, and use the etching solution to erode the pattern area on the substrate material according to the design requirements, and transfer the pattern defined by the photoresist to the substrate material.

[0093] The method of setting the edge of the gate of the selection tube on the geometric center line of the word line and making the gate symmetrical with the word line during the processing includes the following steps:

[0094] Step 2.1: Design word line pattern and select transistor gate pattern: First, design the word line pattern in the electronic design automation software so that the geometric center line of the word line is clear and measurable; then, design the select transistor gate pattern in the EDA software so that its edge is aligned with the geometric center line of the word line pattern;

[0095] Step 2.2: Photolithography alignment: Use the high-precision alignment system of the photolithography machine to align the substrate material with the photolithography mask on the photolithography machine to accurately align the word line with the gate pattern of the selection tube.

[0096] The method of covering different numbers of word lines on the gate of the selection tube comprises the following steps:

[0097] Step 3.1: Determine the coverage strategy: Select the design of the gate pattern as described in step 2.1 so that it can cover different numbers of word lines as needed;

[0098] Step 3.2: Implement word line coverage: Figure 5 , Figure 6As shown, the selection tube pattern covers the enhanced protection word line, and the edge word line and the selection tube ensure that the morphology, size, distance, uniformity and edge roughness meet the process requirements. The covering method is: forming a first word line on the selection tube gate, and the first word line covers a partial area of ​​the selection tube gate, and the partial area refers to setting the coverage ratio and width according to design requirements, rather than full coverage; forming a second word line on the first word line, the second word line covers a partial area of ​​the first word line, and the width of the second word line is different from that of the first word line; forming a third word line on the second word line, the third word line covers a partial area of ​​the second word line, and the width of the third word line is different from that of the second word line; repeating the above steps until the required number of word lines are formed on the selection tube gate.

[0099] The method of removing the word line sacrificial layer to make the word line independent of other structures comprises the following steps:

[0100] Step 4.1: Sacrificial layer design: Figure 1 , Figure 4 , Figure 5 As shown, due to the sparse exposure environment, regular edge word lines are prone to process defects such as line inversion, overexposure, and sidewall formation defects, causing the edge word line morphology, size, uniformity, and edge roughness to exceed the allowable range; after completing the coverage of the selection tube gate in the previous step, a sacrificial layer is designed and formed above the word line according to the design requirements;

[0101] Step 4.2: Formation of sacrificial layer and protective layer: After the above steps of designing the sacrificial layer are completed, a sacrificial layer is formed on the word line using chemical vapor deposition and physical vapor deposition methods according to the design results; after the sacrificial layer is formed, a protective layer needs to be formed on the sacrificial layer;

[0102] Step 4.3: Removal of sacrificial layer: Figure 2 As shown, a plasma etching process is used to remove the sacrificial layer; the removal method steps are as follows: first, the etching rate and the position of the sacrificial layer are determined, and while performing the etching process, the etching rate and depth are monitored; Figure 4 As shown, after the sacrificial layer is removed, the independent word line is exposed, and then a protective layer is added on the word line. The advantage is that the regular edge word line has an enhanced protective word line, and the exposure environment is improved. The process defects such as inverted line, overexposure, and side wall formation defects that appeared in the original process are significantly improved, ensuring that the morphology, size, uniformity, distance and edge roughness of the regular edge word line are within a controllable range.

[0103] The subsequent etching of the selection tube gate, transferring the pattern of the selection tube gate to the substrate material after the etching is completed, and cutting the head and tail word lines include the following steps:

[0104] Step 5.1: Select the tube grid pattern to transfer: First, Figure 1 , Figure 2 As shown, after removing the sacrificial layer, on the basis of the selection tube grid already formed on the substrate material, the pattern of the selection tube grid is prepared by using electron beam lithography technology, and then the selection tube grid is etched by plasma etching technology, and the pattern is transferred to the substrate material to form the desired three-dimensional structure;

[0105] Step 5.2: Word line cutting: Figure 3 , Figure 4 , Figure 7 As shown, due to the existence of enhanced protection word lines, the process defects of regular edge word lines, such as line inversion, overexposure, and side wall formation defects, which appeared in the original process, are significantly improved; then according to the design requirements, the specific position of word line cutting is first determined, and then the cutting path and mode are set in the cutting area, and the cutting parameters are adjusted, and finally the cutting operation is performed using plasma cutting technology.

[0106] After the etching and word line cutting steps are completed, the final pattern of the selection tube is defined by the selection tube exposure pattern at the edge away from the word line direction, including the following contents:

[0107] Step 6.1: Exposure pattern preparation: First, according to the design requirements of the selection tube, use the CAD tool to design the outer edge pattern of the selection tube that meets the design requirements, then evenly coat the photoresist on the substrate material, and use the drying program to control the thickness and quality of the photoresist;

[0108] Step 6.2: Exposure and development: After the exposure pattern is prepared, the photoresist-coated substrate material is exposed using a photolithography machine, the exposure dose and resolution are controlled, and the outer edge pattern of the selected tube is matched with the design pattern; after exposure, the substrate material is placed in a developer for development operation;

[0109] Step 6.3: Etching the edge of the selector: After the exposure and development steps are completed, according to the design requirements, the edge of the selector gate away from the word line direction needs to be etched; and the shape and size of the selector gate are controlled by adjusting the etching rate.

[0110] The method of defining the final pattern of the selection tube by the edge of the word line overlapping the selection tube exposure pattern in the direction close to the word line includes the following steps:

[0111] Step 7.1: Photolithography process: Place the mask with the exposure pattern of the selector tube on the wafer for exposure processing, then put the exposed wafer into the developer to form the pattern of the selector tube, and finally use the etching solution to etch away the part not protected by the photoresist to form the structure of the selector tube on the wafer;

[0112] Step 7.2: Alignment and overlap check: In the overlapping area of ​​the select tube and the word line, and in the direction close to the word line, the pattern of the select tube matches the edge of the word line. The high-precision alignment system of the lithography machine is required to confirm the alignment of the exposure pattern of the select tube with the word line, and check the overlap between the two.

[0113] The final pattern of the selection tube and the distance between the word lines are defined by the word line exposure layer and include the following steps:

[0114] Step 8.1: Adjust the size of the exposure layer pattern: According to the design requirements, use electron beam lithography technology to control the size of the exposure layer pattern according to the design parameters, then use computer-aided design software to accurately design the exposure layer pattern, and use the high resolution capability of the lithography machine to transfer the design pattern to the exposure layer; calculate the size of the exposure layer pattern using the following formula:

[0115] L=D+σ L

[0116] Where D represents the distance between the selection tube and the word line according to the design requirements, L represents the size of the exposure layer pattern, σ L Represents the margin reserved to take into account process deviations;

[0117] Taking into account the optical diffraction effect in the photolithography process, the size of the exposure layer pattern can be corrected by the following formula:

[0118] L′=L+λsin(t)

[0119] Wherein, L′ represents the corrected exposure layer pattern size, λ represents the photolithography wavelength, and t represents the diffraction angle;

[0120] The above formula takes into account factors such as process deviation. To ensure that the final pattern size meets the design requirements, a correction term is added to adjust the size of the exposure layer pattern to compensate for the size change caused by diffraction.

[0121] Assuming that the distance between the selection tube and the word line required by the design is 100nm, the reserved margin is 10nm, the lithography wavelength is 193nm, and the diffraction angle is 0.1 radian, the size of the exposure pattern is:

[0122] L=D+σ L

[0123] =100+10

[0124] =110nm

[0125] Then the corrected exposure layer graphic size is:

[0126] L′=L+λsin(t)

[0127] =110+193·s in(0.1)

[0128] ≈116nm

[0129] Through electron beam lithography technology and the high resolution of the lithography machine, precise control of the pattern size can be achieved, while corrections can be made considering the optical diffraction effect to ensure more accurate spacing control;

[0130] Step 8.2: Adjust the exposure layer pattern position: After the exposure layer pattern size design is completed, the exposure layer position is fine-tuned in the horizontal and vertical directions, and then the alignment system of the lithography machine is used to control the spacing between the two through mechanical positioning and alignment; and phase shift exposure technology is used at the same time to confirm the position and spacing of the pattern;

[0131] For fine-tuning the exposure layer position, the new exposure layer position can be calculated using the following formula:

[0132] X′=X+σ X

[0133] Where X is the original exposure layer position, X′ is the new exposure layer position, σ X For fine-tuning amount;

[0134] Taking into account the accuracy and error of the lithography machine alignment system, the following formula can be used to correct the position of the exposure layer:

[0135] X″=X′+ε

[0136] Where X″ represents the position of the corrected exposure layer, and ε represents the error of the alignment system of the lithography machine;

[0137] However, phase-shifted exposure can be achieved by adjusting the exposure dose and phase, and the position of the pattern after exposure can be calculated by the following formula:

[0138] X″′=X″+I·cos(ψ)

[0139] Where X″′ represents the position of the pattern after exposure, I represents the exposure dose, and ψ represents the phase shift.

[0140] This formula indicates that the position and spacing control of the pattern is optimized by phase-shift exposure, and the position of the pattern after exposure is adjusted by adding a term related to the exposure dose and phase;

[0141] Assuming that the exposure layer needs to be fine-tuned 5nm to the right in the horizontal direction, the alignment error of the lithography machine is 1nm, the exposure dose is 100mj / cm2, and the phase offset is 0.2 radians, the position of the new exposure layer should be:

[0142] X′=X+σ X

[0143] =X+5

[0144] =5nm

[0145] X″=X′+ε

[0146] =5+1

[0147] =6nm

[0148] X″′=X″+I·cos(ψ)

[0149] =6+100·cos(0.2)

[0150] ≈103nm

[0151] Through the precise mechanical positioning and alignment of the lithography machine alignment system and the change of phase offset exposure, the position of the exposure layer can be fine-tuned, thereby more accurately controlling the spacing between the selection tube and the word line.

[0152] The method of covering the edge word line with the selection tube and transferring the non-uniformity of the edge word line to the internal word line comprises the following steps:

[0153] Step 9.1: Edge word line design: After the exposure layer size and position adjustment are completed and the distance between the final pattern of the tube and the word line is confirmed, the layout and shape of the edge word line are designed according to the design requirements;

[0154] Step 9.2: Selector tube layout: After the edge word line design is completed, the size and shape of the selector tube are planned according to the design requirements of the edge word line, and the position and layout of the selector tube are further arranged;

[0155] Step 9.3: Non-uniformity transfer mechanism: After the edge word line design and selection tube layout are completed according to the above steps, after the edge word line is covered by the selection tube, the edge word line and the selection tube are analyzed for non-uniformity using an electrical test method to confirm the existing non-uniformity characteristics and distribution;

[0156] Assume that there is a batch of NAND flash memory chip samples. First, the edge word line resistance of each chip is tested using the four-point probe method. During the test, ensure that the probe is in good contact with the word line and record the resistance value of each test point. Perform multiple tests on the edge word line of each chip and organize and store the test data.

[0157] Then, data analysis is performed to calculate statistical parameters such as the average value, standard deviation, maximum value, and minimum value of the edge word line resistance of each chip. By comparing the statistical parameters of different chips, the degree of non-uniformity of the edge word line resistance is evaluated;

[0158] Assuming that the resistance non-uniformity of the edge word line is caused by process deviation during the manufacturing process, the resistance value is higher in the edge area of ​​the chip and lower in the inner area.

[0159] Step 9.4: Transfer to internal word lines: Based on the analysis result of the non-uniformity mechanism, the non-uniformity is transferred by establishing a physical connection between the edge word lines and the internal word lines.

[0160] According to the above non-uniformity analysis results, it is assumed that the resistance variation range of the edge word line is 100Ω to 200Ω, and the target resistance variation range of the internal word line is 50Ω to 100Ω; through the result analysis, it is decided to use the resistance network transfer mechanism to achieve the transfer of non-uniformity. The resistance network can simulate the resistance variation of the edge word line by adjusting the resistance value and map it to the internal word line;

[0161] Based on the above assumed data, a proportionality coefficient K can be defined such that

[0162] K = (variation range of internal word line resistance) / (variation range of edge word line resistance)

[0163] Substituting the data, we get

[0164] K=(100Ω-50Ω) / (200Ω-100Ω)=0.5

[0165] Then for each resistance value R of the edge word line, we can calculate the resistance value r of the internal word line by the following formula:

[0166] r=R·K

[0167] Assuming the resistance of the edge word line is 150Ω, the resistance of the internal word line is:

[0168] r=150Ω·0.5=75Ω

[0169] In this way, we can calculate the resistance value of the corresponding internal word line according to the resistance value of the edge word line, thereby realizing the transfer of the non-uniformity.

[0170] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for improving the uniformity of NAND block word lines and select tubes, characterized in that: The following steps are involved: Step 1: In the NAND block, there are word lines and select tubes, both of which are gates of the series channel of the NAND block. The pattern of the select tube gate is transferred to the substrate material using photolithography technology, and then the pattern is converted into a three-dimensional structure through etching technology; Step 2: During the layout design stage, the edge of the selector gate is set on the geometric center line of the word line, and the gate and the word line are made symmetrical during the processing; Step 3: Cover different numbers of word lines on the select tube gate according to the design requirements of NAND; Step 4: remove the word line sacrificial layer. The sacrificial layer is a temporary layer used to protect the word line in subsequent processing steps. After removing the sacrificial layer, the word line can be independent of other structures. Step 5: Perform subsequent etching on the gate of the selection tube. After the etching is completed, the pattern of the gate of the selection tube is transferred to the substrate material, and the head and tail word lines are cut off; Step 6: After the etching and word line cutting steps are completed, the final pattern of the selection tube is defined by the selection tube exposure pattern at the edge away from the word line direction; Step 7, for the portion where the selection tube overlaps with the word line, in the direction close to the word line, the final pattern of the selection tube is defined by the edge of the word line that overlaps with the exposure pattern of the selection tube; Step 8: According to the results of Step 7 and Step 8, the distance between the final pattern of the selection tube and the word line is defined by the word line exposure layer. The distance between the selection tube and the word line is controlled by adjusting the size and position of the exposure layer. Step 9: After the exposure layer position and size are adjusted, the edge word lines are covered with selection tubes to transfer the non-uniformity of the edge word lines to the internal word lines.

2. The method for improving the uniformity of NAND block word lines and select tubes according to claim 1, characterized in that: The method of transferring the pattern of the selector gate to the substrate material by using the photolithography technology and then converting the pattern into a three-dimensional structure by using the etching technology includes the following steps: Step 1.1: Making an insulating layer: Select a base material, clean and treat the surface, and make a layer of insulating material on the base material as an insulating layer for the gate of the selection tube; Step 1.2: Manufacturing photolithography mask: First, use electronic design automation tools to design the pattern of the selection tube gate and generate a photolithography mask pattern, and then manufacture the photolithography mask according to the designed pattern; Step 1.3: Photolithography step: Place the manufactured photolithography mask on the substrate material, and use light sources of different wavelengths for photolithography according to the photolithography requirements to cause chemical changes in the photoresist in the area corresponding to the mask pattern; Step 1.4: Development step: Place the exposed substrate material into a developer to dissolve the exposed portion of the photoresist to form a pattern of the selector gate; Step 1.5: Etching step: Place the developed substrate material into an etching solution, and use the etching solution to erode the pattern area on the substrate material according to the design requirements, and transfer the pattern defined by the photoresist to the substrate material.

3. The method for improving the uniformity of NAND block word lines and select tubes according to claim 1, characterized in that: The method of setting the edge of the gate of the selection tube on the geometric center line of the word line and making the gate symmetrical with the word line during the processing includes the following steps: Step 2.1: Design word line pattern and select transistor gate pattern: First, design the word line pattern in the electronic design automation software so that the geometric center line of the word line is clear and measurable; then, design the select transistor gate pattern in the EDA software so that its edge is aligned with the geometric center line of the word line pattern; Step 2.2: Photolithography alignment: Use the high-precision alignment system of the photolithography machine to align the substrate material with the photolithography mask on the photolithography machine to accurately align the word line with the gate pattern of the selection tube.

4. The method for improving the uniformity of NAND block word lines and select tubes according to claim 3, characterized in that: The method of covering different numbers of word lines on the gate of the selection tube comprises the following steps: Step 3.1: Determine the coverage strategy: According to the design of the gate pattern of the selection tube described in step 2.1 of claim 3, it can cover different numbers of word lines as needed; Step 3.2: Implement word line coverage: Form a first word line on the selection tube gate, and the first word line covers a partial area of ​​the selection tube gate, and the partial area refers to setting the coverage ratio and width according to design requirements, rather than full coverage; Form a second word line on the first word line, the second word line covers a partial area of ​​the first word line, and the width of the second word line is different from that of the first word line; Form a third word line on the second word line, the third word line covers a partial area of ​​the second word line, and the width of the third word line is different from that of the second word line; Repeat the above steps until the required number of word lines are formed on the selection tube gate.

5. The method for improving the uniformity of NAND block word lines and select tubes according to claim 1, characterized in that: The method of removing the word line sacrificial layer to make the word line independent of other structures comprises the following steps: Step 4.1: Sacrificial layer design: After completing the coverage of the selector gate in the previous step, design and form a sacrificial layer above the word line according to the design requirements; Step 4.2: Formation of sacrificial layer and protective layer: After the above steps of designing the sacrificial layer are completed, a sacrificial layer is formed on the word line using chemical vapor deposition and physical vapor deposition methods according to the design results; after the sacrificial layer is formed, a protective layer needs to be formed on the sacrificial layer; Step 4.3: Removing the sacrificial layer: Use a plasma etching process to remove the sacrificial layer; the removal method steps are as follows: first determine the etching rate and the position of the sacrificial layer, and monitor the etching rate and depth while performing the etching process; when the sacrificial layer is removed, further remove the protective layer to expose the independent word line.

6. The method for improving the uniformity of NAND block word lines and select tubes according to claim 1, characterized in that: The subsequent etching of the selection tube gate, transferring the pattern of the selection tube gate to the substrate material after the etching is completed, and cutting the head and tail word lines include the following steps: Step 5.1: Transferring the pattern of the selector grid: First, on the basis of the selector grid formed on the substrate material, the pattern of the selector grid is prepared by using electron beam lithography technology, and then the selector grid is etched by plasma etching technology to transfer the pattern to the substrate material to form the desired three-dimensional structure; Step 5.2: Word line cutting: According to the design requirements, first determine the specific location of the word line cutting, then set the cutting path and mode in the cutting area, adjust the cutting parameters, and finally use plasma cutting technology to perform the cutting operation.

7. The method for improving the uniformity of NAND block word lines and select tubes according to claim 1, characterized in that: After the etching and word line cutting steps are completed, the final pattern of the selection tube is defined by the selection tube exposure pattern at the edge away from the word line direction, including the following contents: Step 6.1: Exposure pattern preparation: First, according to the design requirements of the selection tube, use the CAD tool to design the outer edge pattern of the selection tube that meets the design requirements, then evenly coat the photoresist on the substrate material, and use the drying program to control the thickness and quality of the photoresist; Step 6.2: Exposure and development: After the exposure pattern is prepared, a photolithography machine is used to expose the substrate material coated with photoresist, and the exposure dose and resolution are controlled to match the outer edge pattern of the selected tube with the design pattern; After exposure, the base material is placed in a developer for development operation; Step 6.3: Etching the edge of the selector tube: After the exposure and development steps are completed, the edge of the selector tube gate away from the word line direction needs to be etched according to the design requirements; The shape and size of the selector gate are controlled by adjusting the etching rate.

8. The method for improving the uniformity of NAND block word lines and select tubes according to claim 1, characterized in that: The method of defining the final pattern of the selection tube by the edge of the word line overlapping the selection tube exposure pattern in the direction close to the word line includes the following steps: Step 7.1: Photolithography process: Place the mask with the exposure pattern of the selector tube on the wafer for exposure processing, then put the exposed wafer into the developer to form the pattern of the selector tube, and finally use the etching solution to etch away the part not protected by the photoresist to form the structure of the selector tube on the wafer; Step 7.2: Alignment and overlap check: In the overlapping area of ​​the select tube and the word line, and in the direction close to the word line, the pattern of the select tube matches the edge of the word line. The high-precision alignment system of the lithography machine is required to confirm the alignment of the exposure pattern of the select tube with the word line, and check the overlap between the two.

9. The method for improving the uniformity of NAND block word lines and select tubes according to claim 1, characterized in that: The final pattern of the selection tube and the distance between the word lines are defined by the word line exposure layer and include the following steps: Step 8.1: Adjust the size of the exposure layer pattern: According to the design requirements, use electron beam lithography technology to control the size of the exposure layer pattern according to the design parameters, then use computer-aided design software to accurately design the exposure layer pattern, and use the high resolution capability of the lithography machine to transfer the design pattern to the exposure layer; calculate the size of the exposure layer pattern using the following formula: L=D+σ L Where D represents the distance between the selection tube and the word line according to the design requirements, L represents the size of the exposure layer pattern, σ L Represents the margin reserved to take into account process deviations; Taking into account the optical diffraction effect in the photolithography process, the size of the exposure layer pattern can be corrected by the following formula: L′=L+λsin(t) Wherein, L′ represents the corrected exposure layer pattern size, λ represents the photolithography wavelength, and t represents the diffraction angle; Step 8.2: Adjust the exposure layer pattern position: After the exposure layer pattern size design is completed, the exposure layer position is fine-tuned in the horizontal and vertical directions, and then the alignment system of the lithography machine is used to control the spacing between the two through mechanical positioning and alignment; and phase shift exposure technology is used at the same time to confirm the position and spacing of the pattern; For fine-tuning the exposure layer position, the new exposure layer position can be calculated by the following formula: X′=X+σ X Where X is the original exposure layer position, X′ is the new exposure layer position, σ X For fine-tuning amount; Taking into account the accuracy and error of the lithography machine alignment system, the following formula can be used to correct the position of the exposure layer: X″=X′+ε Where X″ represents the position of the corrected exposure layer, and ε represents the error of the alignment system of the lithography machine; However, phase-shifted exposure can be achieved by adjusting the exposure dose and phase, and the position of the pattern after exposure can be calculated by the following formula: X″′=X″+I·cos(ψ) Where X″′ represents the position of the pattern after exposure, I represents the exposure dose, and ψ represents the phase shift.

10. The method for improving the uniformity of NAND block word lines and select tubes according to claim 1, characterized in that: The method of covering the edge word line with the selection tube and transferring the non-uniformity of the edge word line to the internal word line comprises the following steps: Step 9.1: Edge word line design: After the exposure layer size and position adjustment are completed and the distance between the final pattern of the tube and the word line is confirmed, the layout and shape of the edge word line are designed according to the design requirements; Step 9.2: Selector tube layout: After the edge word line design is completed, the size and shape of the selector tube are planned according to the design requirements of the edge word line, and the position and layout of the selector tube are further arranged; Step 9.3: Non-uniformity transfer mechanism: After the edge word line design and selection tube layout are completed according to the above steps, after the edge word line is covered by the selection tube, the edge word line and the selection tube are analyzed for non-uniformity using an electrical test method to confirm the existing non-uniformity characteristics and distribution; Step 9.4: Transfer to internal word lines: Based on the analysis result of the non-uniformity mechanism, the non-uniformity is transferred by establishing a physical connection between the edge word lines and the internal word lines.

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