A method for improving the defocus of the photolithography pattern on a mask

Abstract

The present invention provides a method for improving the defocus of photolithographic patterns on a mask. A mask glass substrate without any deposited light-shielding material is provided. According to the graphic design layout of the product, the glass substrate in the regions corresponding to the photolithographic patterns with different focus values on the mask is etched, and the difference in etching depth between regions is kept consistent with the difference in focus values between the corresponding photolithographic patterns. A light-shielding material is deposited on the etched mask glass substrate. According to the graphic design layout of the product, the mask is exposed and etched to transfer the pattern onto the mask, obtaining the prepared mask. The prepared mask is used to expose the wafer, transferring the pattern on the prepared mask onto the wafer. The critical dimensions of the photolithographic patterns are measured by a line width measurement scanning electron microscope to detect whether the photolithographic patterns in regions with different photoresist thicknesses on the wafer surface are all at the optimal exposure position. If there are differences in the optimal focus values of some photolithographic patterns, the etching depth of the mask glass substrate needs to be adjusted according to the measurement results.

Description

Technical Field

[0001] The invention relates to the field of semiconductor technology, and in particular to a method for improving the defocus of mask lithography patterns. Background Art

[0002] Among a series of processes in semiconductor manufacturing, photolithography is a key process in integrated circuit manufacturing. Photolithography uses photochemical reactions to transfer the pattern prepared on the mask to the photoresist film through processes such as primer coating on the wafer surface, spin coating of photoresist, soft baking, alignment, exposure, post-baking, development, hard baking, and testing, so as to make subsequent selective etching and ion implantation possible. In the manufacture of integrated circuits, especially in the back-end dual Damascus trench structure manufacturing process, due to the uneven density of the front layer pattern, uneven coating of the filling material is prone to occur. Due to the uneven distribution of the front layer pattern or the difference in the thickness of the thin film deposition on the wafer surface, the flatness of the current layer of photolithography filling material coating is poor, and there is a difference in the best focus value between the photolithography patterns. During photolithography exposure, the exposure focus of a single exposure area is fixed and it is impossible to fully take into account the uneven photolithography material, resulting in defocusing of some of the patterns exposed on the wafer, affecting the product yield.

[0003] Figure 1 The figure is a cross-sectional diagram of the height difference of the photoresist coating of the current layer due to the different density of the current pattern, and a schematic diagram of the difference in the best focus value between the photolithography patterns. The thickness of the photoresist material varies due to the inconsistent degree of solvent evaporation when baking the photoresist in the pattern-dense area and the isolated pattern area. In theory, the thickness of the photoresist is uneven, and the best exposure focus will deviate when exposing photoresists of different thicknesses. However, the exposure focus of a single exposure area cannot be changed dynamically in real time during exposure by the exposure machine, so it is easy for some patterns to be out of focus due to the inconsistency between the focus set by the exposure system and the best exposure focus of the pattern. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a method for improving the defocus of a mask lithography pattern, so as to solve the defocus problem of the lithography pattern in the prior art caused by the difference in density of the previous layer pattern.

[0005] To achieve the above-mentioned and other related purposes, the present invention provides a method for improving the defocus of a mask lithography pattern, which at least comprises:

[0006] Step 1, providing a mask glass substrate without depositing any material;

[0007] Step 2: According to the graphic design layout of the product, etch the glass substrate in the regions corresponding to the lithography patterns with different focus values on the mask plate. The difference in etching depth between regions is consistent with the difference in focus values between the corresponding lithography patterns. Light rays with different etching depths passing through the mask plate form different focal planes due to the optical path difference, thereby obtaining the lithography patterns with different focus values;

[0008] Step 3: Deposit a light-shielding material on the etched glass substrate of the mask plate;

[0009] Step 4: According to the graphic design layout of the product, expose and etch the mask plate deposited with the light-shielding material to transfer the pattern onto the mask plate, obtaining the prepared mask plate;

[0010] Step 5: Use the prepared mask plate to expose the wafer and transfer the pattern on the prepared mask plate onto the wafer;

[0011] Step 6: Measure the critical dimensions of the lithography patterns using a line width measurement scanning electron microscope, and detect whether the lithography patterns in different photoresist thickness regions on the wafer surface are all at the optimal exposure position. If there are differences in the optimal focus values of some lithography patterns, it is necessary to return to Step 2 and adjust the etching depth of the mask plate according to the measurement results.

[0012] Preferably, the glass substrate of the mask plate in Step 1 is a quartz glass substrate.

[0013] Preferably, the light-shielding material in Step 3 is completely light-impermeable.

[0014] Preferably, the light-shielding material in Step 3 is a phase-shifting material with a light transmittance and a 180° phase shift for the transmitted light.

[0015] Preferably, the prepared mask plate obtained in Step 4 includes a bipolar mask plate and a phase-shifting mask plate.

[0016] Preferably, in Step 2, different depths of etching are performed on the corresponding regions of the quartz glass substrate according to the focus value differences of the lithography patterns, and different focal planes are formed through the optical path difference.

[0017] Preferably, in Step 4, the quartz glass substrate deposited with the light-shielding material is exposed and etched according to the graphic design layout of the product, and the required pattern is transferred onto the quartz glass substrate. The etching depth of the quartz glass substrate has a one-to-one correspondence with the difference in the optimal exposure focus between the lithography patterns.

[0018] As described above, the method for improving the defocus of photolithography patterns on a mask has the following beneficial effects: By etching the quartz glass substrate of the mask to different depths, there is an optical path difference between the light rays passing through different etched-depth regions, so that the light rays passing through each region of the mask have different focusing values on the wafer, enabling photolithography patterns with different focusing values caused by differences in the density of the previous layer patterns to all be at the optimal focusing value, having the maximum depth of focus, improving the defocus phenomenon of photolithography patterns caused by differences in the density of the previous layer patterns, and increasing the product yield. Description of the Drawings

[0019] Figure 1 Showing a cross-sectional view of the height difference in photoresist coating of the current layer caused by different densities of the current layer patterns in the prior art;

[0020] Figure 2 Showing a schematic diagram of preparing a mask with a glass substrate of different etched depths according to the present invention;

[0021] Figure 3 Showing a schematic diagram of mask exposure preparation in the present invention;

[0022] Figure 4 Showing a flowchart of the method for improving the defocus of photolithography patterns on a mask in the present invention. Detailed Embodiments

[0023] The following specifically illustrates the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0024] Please refer to Figures 1 to 4 . It should be noted that the diagrams provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the diagrams, rather than being drawn according to the number, shape, and size of the components during actual implementation. The type, quantity, and ratio of each component during actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0025] The present invention provides a method for improving the defocus of photolithography patterns on a mask, as Figure 4 shown, Figure 4 which at least includes:

[0026] Furthermore, in step one of this embodiment of the present invention: Provide a mask glass substrate without depositing any material;

[0027] Furthermore, in the present invention, the mask glass substrate in step one of this embodiment is a quartz glass substrate.

[0028] Step Two: According to the graphic design layout of the product, etch the glass substrate in the regions corresponding to the lithography patterns with different focus values on the mask. The difference in etching depth between regions is consistent with the difference in focus values between the corresponding lithography patterns. The light passing through the mask with different etching depths forms different focal planes due to the optical path difference, thereby obtaining the lithography patterns with different focus values.

[0029] Furthermore, in the present invention, in step two of this embodiment, different depths of etching are performed on the corresponding regions of the quartz glass substrate according to the focus value differences of the lithography patterns, and different focal planes are formed through the optical path difference.

[0030] Step Three: Deposit a light-shielding material on the etched mask glass substrate.

[0031] Furthermore, in the present invention, the light-shielding material in step three is completely light-impermeable.

[0032] Furthermore, in the present invention, the light-shielding material in step three is a phase-shifting material with a light transmittance and a 180° phase shift for the transmitted light.

[0033] Step Four: According to the graphic design layout of the product, expose and etch the mask deposited with the light-shielding material, transfer the pattern to the mask, and obtain the prepared mask; as Figure 2 shown, Figure 2 This shows a schematic diagram of preparing a mask with a glass substrate having different etching depths in the present invention.

[0034] Furthermore, in the present invention, the prepared mask obtained in step four of this embodiment includes a bipolar mask and a phase-shifting mask.

[0035] Furthermore, in the present invention, in step four of this embodiment, the quartz glass substrate deposited with the light-shielding material is exposed and etched according to the graphic design layout of the product, and the required pattern is transferred to the quartz glass substrate. The etching depth of the quartz glass substrate has a one-to-one correspondence with the difference in the best exposure focus between the lithography patterns.

[0036] Step Five: Use the prepared mask to expose the wafer and transfer the pattern on the prepared mask to the wafer. Figure 3 This shows a schematic diagram of exposing the prepared mask in the present invention.

[0037] Step 6. Measure the critical dimensions of the lithography pattern using a line-width measurement scanning electron microscope, and detect whether the lithography patterns in different photoresist height regions on the wafer surface are all at the optimal exposure position. If there are differences in the optimal focus values of some of the lithography patterns, it is necessary to return to Step 2 and adjust the etching depth of the mask according to the measurement results.

[0038] The purpose of the present invention is to design a mask for improving the defocus phenomenon of lithography patterns, which can obtain different focal planes simultaneously during one exposure, so that lithography patterns with different focus values are all at the optimal exposure position, ensuring that all lithography patterns have the maximum depth of focus. The above steps can also be mainly described as including the following steps: 1) Prepare a high-quality quartz glass substrate for the mask without depositing any material; 2) According to the graphic design layout of the product, etch the quartz glass substrate in the regions of the mask where the lithography patterns with different focus values are located. The difference in etching depth between regions is consistent with the difference in focus values between the corresponding lithography patterns. The light passing through the quartz glass substrate with different etching depths will form different focal planes due to the optical path difference, so as to obtain lithography patterns with different focus values; 3) Deposit a mask light-shielding material on the etched quartz glass substrate. The light-shielding material used can be completely opaque or a phase-shifting material with a certain light transmittance and a 180° phase shift for the transmitted light; 4) According to the graphic design layout of the product, expose and etch the quartz glass substrate deposited with the light-shielding material to transfer the required pattern to the mask. The prepared mask includes a bipolar mask and a phase-shifting mask; 5) Use the prepared mask to expose the wafer and transfer the pattern on the mask to the wafer; 6) Measure the critical dimensions of the lithography pattern using a line-width measurement scanning electron microscope, and detect whether the lithography patterns in different photoresist height regions on the wafer surface are all at the optimal exposure position. If there are differences in the optimal focus values of some patterns, it is necessary to return to Step 2) and adjust the etching depth of the quartz glass substrate according to the measurement results.

[0039] In summary, the present invention etches the quartz glass substrate of the mask to different depths, and there is an optical path difference between the lights passing through different etching depth regions, so that the lights passing through each region of the mask have different focus values on the wafer, making the lithography patterns with different focus values caused by the difference in the density of the front-layer patterns all at the optimal focus value and having the maximum depth of focus, improving the defocus phenomenon of the lithography patterns caused by the difference in the density of the front-layer patterns, and improving the product yield. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0040] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for improving the defocus of the lithographic pattern on a mask, characterized in that, At least including: Step 1: Provide a mask glass substrate without depositing any material; Step 2: According to the graphic design layout of the product, etch the glass substrate in the regions on the mask corresponding to the lithography patterns with different focus values. The difference in etching depth between regions is consistent with the difference in focus values between the corresponding lithography patterns. The light rays with different etching depths passing through the mask form different focal planes due to the optical path difference, thereby obtaining the lithography patterns with different focus values; Step 3: Deposit a light-shielding material on the etched mask glass substrate; Step 4: According to the graphic design layout of the product, expose and etch the mask deposited with the light-shielding material, and transfer the pattern to the mask to obtain the prepared mask; Step 5: Use the prepared mask to expose the wafer and transfer the pattern on the prepared mask to the wafer; Step 6: Measure the critical dimensions of the lithography pattern by a line width measurement scanning electron microscope, and detect whether the lithography patterns in the regions with different photoresist thicknesses on the wafer surface are all at the optimal exposure position. If there is a difference in the optimal focus value of some of the lithography patterns, it is necessary to return to Step 2 and adjust the etching depth of the mask according to the measurement results.

2. The method for improving the defocus of the lithography pattern of the mask according to claim 1, wherein: The mask glass substrate in Step 1 is a quartz glass substrate.

3. The method for improving the defocus of the lithography pattern of the mask according to claim 1, characterized in that: The light-shielding material in Step 3 is completely light-impermeable.

4. The method for improving the defocus of the photolithography pattern of the mask according to claim 1, wherein: The light-shielding material in Step 3 is a phase shift material with a light transmittance and a 180° phase shift for the transmitted light.

5. The method for improving the defocus of the photolithography pattern of the mask according to claim 1, characterized in that: The prepared mask obtained in Step 4 includes a bipolar mask and a phase shift mask.

6. The method for improving the defocus of the lithography pattern of the mask according to claim 1, wherein: In Step 2, the corresponding regions of the quartz glass substrate are etched to different depths according to the focus value difference of the lithography pattern, and different focal planes are formed through the optical path difference.

7. The method for improving the defocus of the mask lithography pattern according to claim 1, wherein: In Step 4, the quartz glass substrate deposited with the light-shielding material is exposed and etched according to the graphic design layout of the product, and the required pattern is transferred to the quartz glass substrate. The etching depth of the quartz glass substrate has a one-to-one correspondence with the difference in the optimal exposure focus between the lithography patterns.

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