Method for correcting phase of phase shift mask

Abstract

This invention provides a method for correcting the phase of a phase-shifting mask, comprising the following steps: providing a phase-shifting mask to be corrected, the phase-shifting mask including a base layer and a phase-shifting layer disposed on the base layer, the phase-shifting layer including a phase-shifting pattern, with a light-transmitting area between adjacent phase-shifting patterns, the light-transmitting area exposing the base layer, and the phase shift of the phase-shifting mask being greater than a predetermined value; forming a photoresist protective layer on the phase-shifting mask, the photoresist protective layer filling the light-transmitting area, and the upper surface of the photoresist protective layer being higher than the upper surface of the phase-shifting layer; thinning the phase-shifting pattern using plasma anisotropic etching, and measuring the phase shift of the thinned phase-shifting mask; if the phase shift does not meet the requirements, repeating plasma anisotropic etching and phase shift measurement until the phase shift of the phase-shifting mask meets the requirements; forming an oxide layer on the surface of the thinned phase-shifting pattern; and removing the photoresist protective layer using a composite acid-free cleaning method, the composite acid-free cleaning method being chemically inert to the oxide layer. The phase shift mask phase correction method of the present invention can accurately thin the phase shift layer to correct the phase shift without affecting the critical dimensions and surface quality of the pattern. At the same time, it ensures that the corrected surface is not corroded by chemical solutions during the subsequent desizing and cleaning process, thereby achieving non-destructive and accurate repair of substandard masks.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit manufacturing, and more particularly to a method for correcting the phase of a phase-shifting mask. Background Technology

[0002] Phase-shifting masks enhance lithography resolution by introducing a phase difference of approximately 180° between adjacent transparent regions. For phase-shifting masks, the thickness of the phase-shifting layer (e.g., a MoSi layer) directly determines the magnitude of the phase shift. During manufacturing, due to fluctuations in deposition and etching processes, the actual thickness of the phase-shifting layer may deviate from the design value, resulting in excessive phase shift.

[0003] Currently, the main methods used in the industry to correct the phase of phase-shifting masks include: SF6 (sulfur hexafluoride) chemical etching is used to deepen the quartz substrate to adjust the phase shift. Specifically, when the phase shift is below the target value (i.e., the quartz trench etching depth is insufficient), SF6 plasma chemical etching is used to further deepen the quartz substrate. The specific process is as follows: the entire phase shift mask is placed in a plasma environment containing SF6. The fluorine radicals (F*) generated by the dissociation of SF6 react chemically with the quartz (SiO2) substrate to generate volatile products such as SiF4, which are then removed. In this correction method, SF6 etches the quartz substrate, which can correct the phase, but it also damages key parameters such as the flatness and transmittance of the quartz substrate, leading to new defects. Furthermore, there is no real-time phase detection method during the etching stage, and parameters can only be preset based on experience. The etching endpoint cannot be accurately determined, and repeated removal, measurement, and re-etching are required for trial and error processing, resulting in low processing efficiency and poor phase control accuracy. In addition, this etching method is an isotropic pure chemical reaction, which inevitably produces lateral drilling, causing transverse erosion of the quartz trench sidewalls, resulting in uncontrollable expansion of the critical dimension (CD).

[0004] The phase-shifting layer was etched using SPM / SC1 chemical cleaning. Specifically, the phase-shifting mask was chemically cleaned using SPM (a mixture of sulfuric acid and hydrogen peroxide) and SC1 (a mixture of ammonia, hydrogen peroxide, and water). The entire phase-shifting mask was sequentially immersed in the SPM and SC1 cleaning solutions. The strong oxidizing SPM system first decomposed and removed organic impurities from the surface, while the alkaline oxidizing SC1 system generated hydroxyl radicals that synergistically etched a uniform, minute amount of chemically into the phase-shifting layer, dissolving and removing excess film material. The soluble byproducts generated during the reaction were removed by rinsing with the overflow. In this correction method, SPM (strong oxidizing acid) and SC1 (strong alkaline oxidizing solution) are originally used for photoresist removal and particle cleaning after mask pattern etching. Both of them will have a non-selective chemical erosion effect on the phase shift layer. Although they can remove organic contaminants on the surface, they will cause irregular thinning and surface roughening of the phase shift layer in the whole photoresist removal and cleaning process, resulting in phase shift and critical dimension (CD) changes, and the phase correction effect will be completely invalidated. In addition, after treatment with SPM and SC1, sulfate and ammonium ion impurities are likely to remain on the mask surface, causing the ion contamination (IC) index to exceed the standard, which greatly increases the probability of haze defects in the subsequent photolithography process, seriously shortens the life of the mask, and simultaneously reduces the yield of batch photolithography processes.

[0005] Therefore, one of the current research focuses is how to precisely thin the phase shift layer to correct the phase shift without affecting the critical dimensions and surface quality of the pattern, while ensuring that the corrected surface is not corroded by chemical solutions during the subsequent desizing and cleaning process, so as to achieve non-destructive and precise repair of the oversized photomask. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a phase correction method for phase shift masks, which can accurately thin the phase shift layer to correct the phase shift without affecting the critical dimensions and surface quality of the pattern, while ensuring that the corrected surface is not corroded by chemical solutions during the subsequent desizing and cleaning process, thereby achieving non-destructive and accurate repair of masks that exceed the standard.

[0007] To address the aforementioned problems, this invention provides a method for correcting the phase of a phase-shifting mask, comprising the following steps: providing a phase-shifting mask to be corrected, the phase-shifting mask comprising a substrate layer and a phase-shifting layer disposed on the substrate layer, the phase-shifting layer comprising a phase-shifting pattern, with a light-transmitting region between adjacent phase-shifting patterns, the light-transmitting region exposing the substrate layer, and the phase offset of the phase-shifting mask being greater than a predetermined value; forming a photoresist protective layer on the phase-shifting mask, the photoresist protective layer filling the light-transmitting region, and the photoresist... The upper surface of the protective layer is higher than the upper surface of the phase shift layer; the phase shift pattern is thinned by plasma anisotropic etching, and the phase shift of the thinned phase shift mask is measured. If the phase shift does not meet the requirements, plasma anisotropic etching and phase shift measurement are repeated until the phase shift of the phase shift mask meets the requirements; an oxide layer is formed on the surface of the thinned phase shift pattern; the photoresist protective layer is removed by a composite acid-free cleaning method, which is chemically inert to the oxide layer.

[0008] In one embodiment, prior to the step of forming a photoresist protective layer on the phase-shifting mask, the method further includes the following steps: obtaining an etching selectivity ratio of the plasma anisotropic etching process for the phase-shifting pattern and the photoresist; the step of forming a photoresist protective layer on the phase-shifting mask further includes: determining the height of the photoresist protective layer based on the etching selectivity ratio and the expected thinning amount of the phase-shifting pattern.

[0009] In one embodiment, the step of forming a photoresist protective layer on the phase-shifting mask further includes: forming a photoresist material layer on the phase-shifting mask, the photoresist material layer filling the light-transmitting area and covering the upper surface of the phase-shifting pattern; performing reverse polarity exposure on the photoresist material layer and performing a development process to remove the photoresist material layer on the upper surface of the phase-shifting pattern, the remaining photoresist material layer in the light-transmitting area serving as the photoresist protective layer.

[0010] In one embodiment, in the step of thinning the phase shift pattern using plasma anisotropic etching, the plasma etching direction is perpendicular to the surface of the phase shift pattern.

[0011] In one embodiment, in the step of thinning the phase shift pattern using plasma anisotropic etching, the etching gas is a chlorine-containing gas or oxygen.

[0012] In one embodiment, the step of measuring the phase shift of the thinned phase shift mask further includes: performing an in-situ phase shift measurement of the thinned phase shift mask in a chamber for performing plasma anisotropic etching.

[0013] In one embodiment, the step of measuring the phase shift of the thinned phase shift mask further includes: removing the thinned phase shift mask out of the chamber where plasma anisotropic etching is performed, and measuring its phase shift offline.

[0014] In one embodiment, the step of thinning the phase shift pattern using plasma anisotropic etching and measuring the phase shift mask after thinning further includes: calculating the required plasma anisotropic etching time or etching amount for the next round based on the difference between the current phase shift and the target value, combined with the pre-calibrated correspondence between etching rate and phase change, then performing plasma anisotropic etching again, and re-measuring the phase shift after etching is completed.

[0015] In one embodiment, the step of forming an oxide layer on the thinned phase-shift patterned surface further includes: forming the oxide layer in a chamber for performing plasma anisotropic etching or in a vacuum chamber connected to the chamber for performing plasma anisotropic etching.

[0016] In one embodiment, the step of forming an oxide layer on the thinned phase-shift pattern surface further includes: treating the thinned phase-shift pattern surface with oxygen plasma to form the oxide layer.

[0017] In one embodiment, the step of removing the photoresist protective layer using a composite acid-free cleaning method further includes: irradiating the photoresist with ultraviolet light to initiate a photolysis reaction; and dissolving the photolyzed photoresist with a tetramethylammonium hydroxide solution.

[0018] In one embodiment, during or after the step of dissolving the photolyzed photoresist with tetramethylammonium hydroxide solution, megasonic ultrasonic-assisted removal of residual photoresist is employed.

[0019] In one embodiment, after the step of removing the photoresist protective layer using a composite acid-free cleaning method, the method further includes: performing key parameter detection on the phase shift mask; if all key parameters meet the requirements, then the phase correction of the phase shift mask is completed.

[0020] In one embodiment, the key parameters include phase offset, key dimensions, transmittance, and surface quality.

[0021] In one embodiment, the step of providing the phase-shifting mask to be corrected further includes: the phase-shifting mask further includes a light-shielding layer disposed in a region of the substrate layer or the phase-shifting layer where light transmission is not required; the step of forming a photoresist protective layer on the phase-shifting mask further includes: the photoresist protective layer is also formed on the light-shielding layer.

[0022] The above technical solution first involves forming a photoresist protective layer that fills the light-transmitting area and ensures its upper surface is higher than the phase-shifting layer. This photoresist shields the substrate layer, effectively preventing substrate etching during subsequent plasma anisotropic etching to thin the phase-shifting pattern. Simultaneously, the anisotropic nature of plasma etching eliminates lateral drilling, thus preserving the critical dimensions of the phase-shifting pattern. Based on this, a closed-loop dynamic feedback system is constructed, cyclically combining plasma anisotropic etching with phase measurement. This achieves precise control over the thinning amount, completely changing the traditional process's reliance on experience-based presets and reverse... The inefficient mode of repeating errors is eliminated; at the same time, an oxide layer is formed on the surface of the phase shift pattern after plasma etching. This step plays a key role in physical isolation. The subsequent composite acid-free cleaning is chemically inert to the oxide layer, which not only avoids the irregular erosion of the phase shift layer and the substrate layer by traditional strong acid and alkali solutions, but also prevents the expansion of critical dimensions and surface roughening. At the same time, the plasma treatment completes cleaning and passivation. Finally, the entire process achieves comprehensive protection of the mask pattern structure, optical performance and cleanliness, and achieves high-precision, non-destructive and accurate repair of substandard masks.

[0023] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered part of the specification. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the steps of a phase-shifting mask phase correction method provided in an embodiment of the present invention; Figure 2 This is a cross-sectional schematic diagram of the phase-shift mask to be corrected in a correction method provided in an embodiment of the present invention; Figure 3 This is a cross-sectional schematic diagram of the photoresist material layer formed on the phase shift mask in a correction method provided by an embodiment of the present invention; Figure 4 This is a cross-sectional schematic diagram of the formation of a photoresist protective layer on a phase-shifting mask in a correction method provided by an embodiment of the present invention; Figure 5 This is a cross-sectional schematic diagram of the phase shift pattern thinned by plasma anisotropic etching in a correction method provided in an embodiment of the present invention; Figure 6 This is a cross-sectional schematic diagram of the oxide layer formed on the surface of the thinned phase shift pattern in a correction method provided in an embodiment of the present invention; Figure 7 This is a cross-sectional schematic diagram of the removal of the photoresist protective layer in a correction method provided in an embodiment of the present invention. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Figure 1 This is a schematic diagram illustrating the steps of a phase-shifting mask phase correction method according to an embodiment of the present invention, as shown below. Figure 1 As shown, an embodiment of the present invention provides a method for correcting the phase of a phase-shifting mask, comprising the following steps: Step S10, providing a phase-shifting mask to be corrected, the phase-shifting mask comprising a substrate layer and a phase-shifting layer disposed on the substrate layer, the phase-shifting layer comprising a phase-shifting pattern, a light-transmitting area between adjacent phase-shifting patterns, the light-transmitting area exposing the substrate layer, and the phase shift of the phase-shifting mask being greater than a predetermined value; Step S11, forming a photoresist protective layer on the phase-shifting mask, the photoresist protective layer filling the light-transmitting area, and the upper surface of the photoresist protective layer... The surface is higher than the upper surface of the phase shift layer; Step S12, the phase shift pattern is thinned by plasma anisotropic etching, and the phase shift of the thinned phase shift mask is measured. If the phase shift does not meet the requirements, the plasma anisotropic etching and phase shift measurement are repeated until the phase shift of the phase shift mask meets the requirements; Step S13, an oxide layer is formed on the surface of the thinned phase shift pattern; Step S14, the photoresist protective layer is removed by a composite acid-free cleaning method, which is chemically inert to the oxide layer.

[0028] The phase correction method for a phase-shifting mask provided in this invention first involves forming a photoresist protective layer that fills the transparent area and ensures its upper surface is higher than the phase-shifting layer. This photoresist shields the substrate layer, effectively preventing substrate etching during subsequent plasma anisotropic etching to thin the phase-shifting pattern. Simultaneously, the anisotropic nature of plasma etching eliminates lateral drilling, thus preserving the critical dimensions of the phase-shifting pattern. Based on this, a closed-loop dynamic feedback system is constructed, cyclically combining plasma anisotropic etching with phase measurement to achieve precise control of the thinning amount, completely transforming traditional processes. The inefficient approach of relying on experience-based presets and repeated trial and error is replaced by a process that forms an oxide layer on the surface of the phase-shifted pattern after plasma etching. This step plays a crucial role in physical isolation, and the subsequent composite acid-free cleaning exhibits chemical inertness to the oxide layer. This avoids the irregular erosion of the phase-shifted layer and the substrate layer by traditional strong acid and alkali solutions, and also prevents the expansion of critical dimensions and surface roughening. At the same time, plasma treatment completes cleaning and passivation. Ultimately, the entire process achieves comprehensive protection of the mask pattern structure, optical performance, and cleanliness, and enables high-precision, non-destructive, and accurate repair of substandard masks.

[0029] The following is combined Figures 2-7 The method for correcting the phase of a phase-shifting mask provided in one embodiment of the present invention will be described in further detail.

[0030] like Figure 1 and Figure 2 As shown, where, Figure 2 This is a cross-sectional schematic diagram of the phase shift mask 100 to be corrected in a correction method provided in an embodiment of the present invention. Step S10: Provide the phase shift mask 100 to be corrected. The phase shift mask 100 includes a base layer 101 and a phase shift layer 102 disposed on the base layer 101. The phase shift layer 102 includes a phase shift pattern 1021. There is a light-transmitting area 1022 between adjacent phase shift patterns 1021. The light-transmitting area 1022 exposes the base layer 101, and the phase shift of the phase shift mask 100 is greater than a predetermined value.

[0031] The phase-shifting mask 100 is a key optical component in the photolithography process of integrated circuit manufacturing. Its principle is to introduce a phase difference of about 180° between adjacent light-transmitting areas 1022 of the mask, and use the interference effect of light to cancel the edge blurring caused by diffraction, thereby significantly improving the photolithography resolution and imaging contrast without changing the exposure wavelength.

[0032] The phase-shifting mask 100 includes a base layer 101 and a phase-shifting layer 102.

[0033] The substrate layer 101 possesses excellent mechanical strength and chemical stability, and exhibits extremely high transmittance at the exposure wavelength. When light penetrates the photomask, the flatness, transmittance uniformity, and internal defect density of the substrate layer 101 have a decisive impact on the linewidth control and yield of the final photolithography pattern. If the substrate layer 101 is damaged during the correction of the phase-shifting photomask 100, new defects will arise.

[0034] In some embodiments, the substrate 101 is a quartz substrate. Quartz substrates have characteristics such as high light transmittance, low coefficient of thermal expansion, excellent chemical inertness, and high hardness, which can ensure photolithography efficiency, dimensional stability, resistance to chemical corrosion, and structural integrity.

[0035] The phase shift layer 102 is disposed on the surface of the substrate layer 101. The phase shift layer 102 includes a phase shift pattern 1021, and a light-transmitting area 1022 is provided between adjacent phase shift patterns 1021, the light-transmitting area 1022 exposing the substrate layer 101. In the photolithography exposure optical path, when the incident light passes through the phase-shifted pattern 1021 region, it passes through the phase-shifted layer 102 film material and the substrate layer 101 in sequence. The light passing through the adjacent transparent area 1022 (i.e., the exposed substrate layer 101 region) only passes through the substrate layer 101 of the same thickness. Since the optical refractive index and extinction coefficient of the phase-shifted pattern 1021 material are inherently different from those of the substrate layer 101, by designing the thickness of the phase-shifted pattern 1021 to match the target exposure wavelength, the light passing through the phase-shifted pattern 1021 can produce a phase difference of exactly 180° (i.e., the target phase offset) compared to the light passing through the substrate layer 101 in the transparent area 1022. At the same time, the light intensity is attenuated. At this time, the two beams of light projected onto the surface of the target semiconductor layer from the edge of the adjacent phase-shifted pattern 1021 will undergo destructive interference, effectively canceling the pattern edge blurring and light intensity crosstalk caused by diffraction effect, improving the contrast of photolithography imaging, and thus achieving subwavelength-level feature size resolution enhancement.

[0036] The thickness of the phase-shift pattern 1021 directly determines the magnitude of the phase shift. In actual manufacturing, fluctuations in the deposition and etching processes of the phase-shift pattern 1021 inevitably occur, causing the actual thickness to deviate from the design value, resulting in an excessive phase shift and degrading the optical performance of the mask, failing to meet the requirements of high-precision chip mass production. Specifically, in this embodiment of the invention, the phase shift of the phase-shift mask 100 to be corrected is greater than a specified value. This specified value refers to the upper limit of the maximum phase shift allowed when the phase-shift mask 100 is working normally; exceeding this limit will lead to a significant decrease in lithographic resolution. Correspondingly, the phase shift of the phase-shift mask 100 to be corrected being greater than the specified value indicates that the actual thickness of the phase-shift pattern 1021 is greater than its set value, which is the theoretical design thickness calculated based on the target phase shift. The positive deviation between the two is precisely the thickness to be removed in this correction. Figure 2 In the process, the phase-shifted pattern 1021 includes a region 1021A that needs to be retained and a region 1021B that needs to be removed.

[0037] The phase-shifting pattern 1021 employs a semi-transparent material with a certain transmittance to simultaneously achieve light intensity modulation and phase modulation between adjacent transparent regions 1022. In some embodiments, the phase-shifting layer 102 is a molybdenum-silicon-based phase-shifting thin film, meaning the material of the phase-shifting pattern 1021 is a molybdenum-silicon-based material. Molybdenum-silicon-based materials refer to alloy thin films composed primarily of molybdenum and silicon, including MoSi2, MoSiON (molybdenum silicon oxynitride), or MoSiN (molybdenum silicon nitride), etc.

[0038] In some embodiments, the phase-shifting mask 100 further includes a light-shielding layer 103, which is disposed in areas of the substrate layer 101 or the phase-shifting layer 102 where light is not required to pass through. The light-shielding layer 103 completely blocks areas of the phase-shifting mask 100 where light is not required to pass through, ensuring that only the designed transparent areas 1022 and the phase-shifting pattern 1021 areas receive light during photolithography exposure, thereby preventing stray light from causing unnecessary exposure of the semiconductor layer. The light-shielding layer 103 is made of a material with an extremely high absorption coefficient for the exposure wavelength, such as chromium or its compounds. The light-shielding layer 103 generally covers the phase-shifting layer 102 or is embedded between the phase-shifting layers 102, with the specific layout depending on the mask design type. The light-shielding layer 103 also needs to be protected in subsequent correction processes, because if the light-shielding layer 103 is accidentally etched or damaged, it will directly cause light leakage defects in the mask during photolithography, leading to fatal circuit failures such as short circuits or open circuits on the wafer.

[0039] like Figure 1 and Figure 4 As shown, where, Figure 4This is a cross-sectional schematic diagram of the correction method provided in an embodiment of the present invention, in which a photoresist protective layer is formed on a phase shift mask 100. In step S11, a photoresist protective layer 400 is formed on the phase shift mask 100. The photoresist protective layer 400 fills the light-transmitting area 1022, and the upper surface of the photoresist protective layer 400 is higher than the upper surface of the phase shift layer 102.

[0040] This step utilizes photoresist to selectively protect the surface of the phase-shifting mask 100, providing a physical basis for subsequent plasma anisotropic etching. Specifically, since the light-transmitting area 1022 exposes the substrate layer 101, if the phase-shifting pattern 1021 is directly etched, the exposed substrate layer 101 will inevitably be bombarded by plasma and chemically eroded, leading to surface roughening, decreased light transmittance, and even microcracks in the substrate layer 101, severely affecting the optical performance and lifespan of the phase-shifting mask 100. Therefore, the substrate layer 101 of the light-transmitting area 1022 is covered with the photoresist protective layer 400 to form a physical barrier, preventing damage during subsequent plasma anisotropic etching.

[0041] Furthermore, the upper surface of the photoresist protective layer 400 is higher than the upper surface of the phase-shifting layer 102. During subsequent plasma anisotropic etching, when the plasma bombards vertically downwards, the photoresist protective layer 400 will be preferentially etched away, while the sidewalls of the phase-shifting pattern 1021 under the photoresist protection remain shielded. This effectively prevents lateral drilling and ensures that the critical dimensions of the pattern do not expand unintended. In addition, the higher upper surface of the photoresist protective layer 400 also provides sufficient margin for thickness loss during the etching process. Even after multiple etching cycles, the photoresist protective layer 400 can continue to provide protection until the phase-shifting pattern 1021 is thinned to the target thickness.

[0042] In some embodiments, the photoresist protective layer 400 is also formed on the light-shielding layer 103, which can ensure that the integrity of the light-shielding layer 103 is not affected during the thinning of the phase-shifting pattern 1021, thereby maintaining the overall optical shielding performance of the photomask.

[0043] Furthermore, before the step of forming the photoresist protective layer 400 on the phase shift mask 100, the following steps are included: obtaining the etching selectivity ratio of the plasma anisotropic etching process for the phase shift pattern 1021 and the photoresist; the step of forming the photoresist protective layer 400 on the phase shift mask 100 further includes: determining the height of the photoresist protective layer 400 based on the etching selectivity ratio and the expected thinning amount of the phase shift pattern 1021.

[0044] This preliminary step, through quantitative process parameter design, ensures that the photoresist protective layer 400 maintains sufficient thickness margin throughout the entire etching cycle, preventing premature depletion of the photoresist and resulting exposure and damage to the sidewalls of the substrate layer 101 or the phase-shifted pattern 1021. Specifically, the etching selectivity ratio refers to the ratio of the etching rate of the phase-shifted pattern 1021 material to that of the photoresist material under the same plasma conditions. Therefore, given the expected thinning amount of the phase-shifted pattern 1021, the minimum initial thickness of the required photoresist can be deduced from the etching selectivity ratio. An additional safety margin is then added to determine the actual coating height of the photoresist protective layer 400. The height of the photoresist protective layer 400 is determined based on the etching selectivity and the expected thinning amount of the phase shift pattern 1021. On the one hand, this avoids unnecessary material waste and increased difficulty in subsequent removal caused by excessively thick photoresist; on the other hand, it can accurately match the etching process, ensuring that the photoresist can still completely cover the substrate layer 101 and the sidewalls of the phase shift pattern 1021 at the last moment when the phase shift pattern 1021 is thinned to the target thickness, thereby achieving full non-destructive protection for the entire etching process.

[0045] In some embodiments, plasma bombardment is applied to the entire surface of the product. During this process, the photoresist protective layer 400 is thinned by the bombardment, but the amount of thinning is negligible relative to the overall height of the photoresist protective layer 400, and therefore does not weaken its protective effect. Simultaneously, the phase-shifted pattern 1021 is thinned by the plasma bombardment, resulting in a phase change. In one embodiment, the thickness of the photoresist protective layer 400 is typically around 400 nm, and the thickness of the phase-shifted layer 102 is typically around 80 nm.

[0046] An embodiment of the present invention also provides a method for forming the photoresist protective layer 400. Specifically, the method includes: like Figure 3 As shown, it is a cross-sectional schematic diagram of the photoresist material layer 300 formed on the phase shift mask 100 in a correction method provided by an embodiment of the present invention. The photoresist material layer 300 is formed on the phase shift mask 100, and the photoresist material layer 300 fills the light-transmitting area 1022 and covers the upper surface of the phase shift pattern 1021.

[0047] Specifically, a layer of photoresist material is uniformly applied to the surface of the phase-shifting mask 100 through a coating process such as spin coating or spray coating. Due to the good fluidity and surface wettability of the photoresist, it will spontaneously flow into the light-transmitting area 1022 between adjacent phase-shifting patterns 1021 during the coating process, completely filling and covering the originally exposed substrate layer 101. At the same time, a continuous thin film is also formed on the upper surface of the phase-shifting pattern 1021 and the upper surface of the light-shielding layer 103.

[0048] like Figure 4As shown, the photoresist material layer 300 is subjected to reverse polarity exposure and a development process is performed to remove the photoresist material layer 300 on the upper surface of the phase shift pattern 1021. The remaining photoresist material layer 300 in the light-transmitting area 1022 serves as the photoresist protective layer 400.

[0049] This step utilizes the positive and negative properties of the photoresist combined with reverse polarity (tone) exposure to achieve selective removal of the photoresist material layer 300. Specifically, reverse polarity exposure refers to using a mask or exposure strategy that is the opposite of conventional photolithography. In conventional positive photoresist, the exposed areas are removed after development, while the unexposed areas are retained; however, reverse polarity exposure uses negative photoresist or flips the mask pattern so that the areas to be retained (i.e., the light-transmitting area 1022) are exposed, thus curing and remaining after development, while the areas to be removed (i.e., the upper surface of the phase-shifted pattern 1021) are dissolved and carried away by the developer due to insufficient or no exposure. In this embodiment, after reverse polarity exposure and development, the photoresist covering the upper surface of the phase-shifted pattern 1021 is completely removed, exposing the top of the phase-shifted pattern 1021, providing a direct working surface for subsequent plasma anisotropic etching; while the photoresist filling the light-transmitting area 1022 and covering the surface of the light-shielding layer 103 is completely preserved due to exposure curing, forming a strong photoresist protective layer 400.

[0050] The photoresist protective layer 400 is tightly adhered to the surface of the substrate layer 101, the surface of the light-shielding layer 103, and the sidewalls of the phase-shift pattern 1021. During subsequent etching, it effectively blocks the vertical bombardment of the substrate layer 101 and the light-shielding layer 103 by plasma and the lateral erosion of the sidewalls of the phase-shift pattern 1021, thereby ensuring that the substrate layer 101 and the light-shielding layer 103 are not damaged and that the critical dimensions of the phase-shift pattern 1021 do not undergo unintended enlargement. Furthermore, since the developing process itself is chemically inert to the phase-shift layer 102 material, the substrate layer 101, and the light-shielding layer 103, it will not cause additional corrosion or contamination, ensuring that the original quality of the mask surface remains unaffected.

[0051] like Figure 1 and Figure 5 As shown, where, Figure 5This is a cross-sectional schematic diagram of the phase shift pattern 1021 thinned by plasma anisotropic etching in a correction method provided by an embodiment of the present invention. In step S12, the phase shift pattern 1021 is thinned by plasma anisotropic etching, and the phase shift mask 100 after thinning is measured. If the phase shift does not meet the requirements, plasma anisotropic etching and phase shift measurement are repeated until the phase shift of the phase shift mask 100 meets the requirements. This etching-measurement closed-loop feedback mechanism ensures that the phase correction accuracy is not limited by empirical preset parameters, and the process endpoint determination is driven by measured data.

[0052] Plasma anisotropic etching is a highly directional dry etching method. It utilizes an electric field to guide active ions in the plasma to accelerate and bombard the surface of the phase-shifted pattern 1021 in a perpendicular direction. That is, the plasma etching direction is perpendicular to the surface of the phase-shifted pattern 1021, thereby achieving top-down layer-by-layer removal of material only from the top of the phase-shifted pattern 1021. As an example, plasma anisotropic etching includes: using chlorine-containing gas or oxygen, combined with an inert diluent gas such as argon, to form a high-density plasma in a low-pressure chamber driven by radio frequency power; by adjusting the bias power, gas flow rate, and chamber pressure, the etching rate and degree of anisotropy can be precisely controlled. Because the top of the phase-shifted pattern 1021 is completely exposed, while the surfaces of the substrate layer 101, the light-shielding layer 103, and the sidewalls of the phase-shifted pattern 1021 remain shielded by the photoresist protective layer 400, the plasma can only act on the upper surface of the phase-shifted pattern 1021, peeling away the excessively thick phase-shifting material layer by layer, gradually bringing the thickness of the phase-shifted pattern 1021 closer to the design value. During this process, the etching rate remains stable and controllable, with the amount of etching per pass typically in the range of several nanometers to tens of nanometers, to avoid excessive thinning. Simultaneously, the anisotropic nature of plasma etching ensures that the perpendicularity of the sidewalls of the phase-shifted pattern 1021 remains unaffected, thus maintaining the original accuracy of critical dimensions and fundamentally eliminating the lateral drilling problem commonly found in traditional SF6 isotropic etching.

[0053] After each plasma anisotropic etching, the phase shift of the thinned phase shift mask 100 is immediately measured. The measurement result is compared with the target phase shift (usually 180°±5°): if the measured value is still outside the allowable tolerance range, it indicates that the thickness of the phase shift pattern 1021 has not reached the design value, and the next round of etching needs to be continued.

[0054] In some embodiments, the step of thinning the phase shift pattern 1021 using plasma anisotropic etching and measuring the phase shift of the thinned phase shift mask 100 further includes: calculating the required plasma anisotropic etching time or etching amount for the next round based on the difference between the current phase shift and the target value, combined with a pre-calibrated correspondence between etching rate and phase change (e.g., each 1 nm of phase shift material etched can reduce the phase shift by approximately 2°~3°). Then, plasma anisotropic etching is performed again, and the phase shift is remeasured after etching. This process is repeated until the phase shift falls within the acceptable range. This closed-loop feedback control mechanism replaces the trial-and-error mode of traditional processes that relies on empirically preset parameters and repeatedly takes out measurements and puts them back for re-etching. This not only significantly improves processing efficiency but also controls the phase correction accuracy within ±1°, achieving efficient and accurate repair of the out-of-specification phase shift mask 100.

[0055] In some embodiments, the phase shift measurement can be performed using an optical phase detector or a laser interferometer. The real-time phase shift value is obtained by comparing the phase difference between two beams of light passing through the phase shift pattern 1021 region and the light-transmitting region 1022 (substrate layer 101). Specifically, before forming the photoresist protective layer 400 on the phase shift mask 100, the phase data of two beams of light passing through the phase shift pattern 1021 region and the light-transmitting region 1022 (i.e., substrate layer 101) are obtained using the aforementioned equipment. The initial phase shift value is obtained by comparing the phase difference between the two beams. In subsequent correction processes, real-time phase detection is performed on the beam passing through the phase shift pattern 1021 region, while the phase data of the light-transmitting region 1022 (substrate layer 101) uses the measurement results before it was covered by the photoresist protective layer 400. Based on this, the real-time phase shift value is calculated.

[0056] Furthermore, in some embodiments, the step of measuring the phase shift of the thinned phase shift mask 100 further includes: performing an in-situ phase shift measurement of the thinned phase shift mask 100 in a chamber for performing plasma anisotropic etching.

[0057] In-situ measurement refers to integrating an optical phase detection module within the same vacuum chamber. After completing a plasma anisotropic etching step, the phase shift mask 100 can be directly and in real-time detected on its surface through an optical window or built-in detection device within the chamber without needing to remove it from the chamber. This significantly shortens the time interval between etching and measurement, avoiding the impact of surface adsorption, temperature changes, or contaminant adhesion caused by atmospheric exposure on measurement accuracy. Simultaneously, since repeated vacuuming and devacuuming operations are eliminated, the process cycle is greatly improved, significantly reducing the correction cycle for a single phase shift mask 100. Furthermore, in-situ measurement data can be directly fed back to the etching control system, enabling real-time adjustment of etching parameters and forming true closed-loop automated control, further improving the consistency and repeatability of phase correction.

[0058] Furthermore, in some embodiments, the step of measuring the phase offset of the thinned phase shift mask 100 further includes: removing the thinned phase shift mask 100 out of the chamber where plasma anisotropic etching is performed, and measuring its phase offset offline.

[0059] Offline measurement refers to removing the phase-shift mask 100 from the etching chamber and transferring it to a dedicated external optical inspection device for phase shift testing. This allows for the use of more precise and feature-rich dedicated phase measurement instruments, resulting in more detailed and accurate phase distribution data. Offline measurement also facilitates the integration of other key parameter measurements on the same equipment, such as critical dimensions, transmittance, and surface roughness, providing multi-dimensional data support for comprehensive evaluation of correction effects. Although offline measurement requires additional handling and transfer steps, potentially extending the process cycle slightly, the rich inspection information it provides is irreplaceable for process verification, first-article inspection, or analysis and troubleshooting of abnormal batches during the R&D phase. Operators can manually or semi-automatically adjust the etching parameters for the next round based on the offline measurement results, achieving high-precision phase correction with relatively simple equipment configuration and low implementation costs.

[0060] like Figure 1 and Figure 6 As shown, where, Figure 6 This is a cross-sectional schematic diagram of forming an oxide layer 600 on the surface of the thinned phase shift pattern 1021 in a correction method provided by an embodiment of the present invention. Step S13: An oxide layer 600 is formed on the surface of the thinned phase shift pattern 1021.

[0061] This step chemically modifies the surface of the freshly exposed phase-shift pattern 1021 to form a dense oxide layer 600. Through this step, the phase-shift pattern 1021 transforms from a highly active etched state to a stable passivated state. Specifically, after plasma anisotropic etching, the top of the phase-shift pattern 1021 is thinned to the target thickness. However, its surface is in a highly active dangling bond state, with loose atomic arrangement and poor chemical stability. If directly exposed to subsequent cleaning solutions, it is prone to irregular chemical erosion, leading to surface roughening, thickness deviation, and changes in critical dimensions. Therefore, this step involves treating the phase-shift mask 100 in an oxygen-containing atmosphere, allowing active oxygen atoms or oxygen free radicals to chemically react with the material on the surface of the phase-shift pattern 1021, generating a continuous, dense, and chemically stable oxide layer 600 in situ.

[0062] The oxide layer 600, acting as a chemically inert barrier, effectively prevents direct contact between the subsequent cleaning solution and the phase-shift pattern 1021 substrate material, avoiding non-selective etching of the phase-shift pattern 1021. Furthermore, the oxide layer 600 itself possesses a certain transmittance and refractive index at the exposure wavelength, and its thickness is extremely thin (typically on the order of several nanometers), contributing negligibly to the overall phase shift and not interfering with the corrected phase accuracy. Simultaneously, the formation process of the oxide layer 600 consumes minimal material from the phase-shift pattern 1021 and does not alter the perpendicularity or critical dimensions of the pattern sidewalls, thus maintaining the integrity of the pattern while achieving surface passivation. In addition, the oxide layer 600 can also serve as a marker layer for identifying corrected areas in subsequent processes, facilitating quality traceability and detection positioning.

[0063] In some embodiments, oxygen plasma is used to treat the thinned surface of the phase-shift pattern 1021 to form the oxide layer 600. Specifically, the thinned phase-shift mask 100 is placed in a plasma processing chamber, and high-purity oxygen is introduced as the reactant gas. Under the excitation of radio frequency power or microwave power, oxygen molecules are dissociated into highly reactive particles such as oxygen atoms, oxygen ions, and oxygen free radicals. These reactive particles move directionally to the surface of the phase-shift pattern 1021 under the action of an electric field, and undergo an oxidation reaction with the material of the phase-shift pattern 1021 to generate a continuous, dense, and stoichiometrically stable oxide film in situ. Oxygen plasma treatment can be performed at low temperatures, avoiding thermal stress deformation of the phase-shift pattern 1021 or thermal reflow of the photoresist protective layer 400 that may be caused by high-temperature oxidation, thus ensuring the overall stability of the mask structure. Furthermore, by adjusting process parameters such as RF power, oxygen flow rate, chamber pressure, and reaction time, the growth thickness of the oxide layer 600 can be precisely controlled, typically limited to the range of 2–10 nanometers. This ensures an effective chemical inert barrier without introducing additional phase shift interference due to excessive oxide layer thickness. Simultaneously, the oxygen plasma itself exhibits an extremely low etching rate on the photoresist protective layer 400 and the substrate layer 101, causing virtually no damage or thinning to these areas. This guarantees the integrity of the photoresist protective layer 400 and the original quality of the substrate layer 101.

[0064] Furthermore, the strong oxidizing environment of oxygen plasma can remove trace amounts of fluoropolymers that may remain during the plasma anisotropic etching process, achieving surface cleaning and providing a clean and uniform surface condition for subsequent resist removal processes.

[0065] Furthermore, in some embodiments, the step of forming an oxide layer 600 on the thinned surface of the phase-shift pattern 1021 further includes: forming the oxide layer 600 in a chamber for performing plasma anisotropic etching or in a vacuum chamber connected to the chamber for performing plasma anisotropic etching, thereby achieving continuous vacuum operation of plasma anisotropic etching and oxidation processes, avoiding exposure of the phase-shift mask 100 to the atmospheric environment between the two processes. Specifically, if the phase-shift mask 100 is directly removed from the etching chamber after plasma anisotropic etching is completed, its highly active dangling bonds will rapidly undergo uncontrollable adsorption or natural oxidation with moisture, oxygen, or organic matter in the environment, resulting in uneven surface conditions, which in turn affects the density and uniformity of the subsequent growth of the oxide layer 600. By directly switching the reaction gas (e.g., from chlorine-containing etching gas to oxygen) within the same chamber or adjacent chambers connected via a vacuum transfer channel, the process transition from etching to oxidation can be completed without breaking the vacuum or contacting the atmosphere. This ensures that the surface of the phase-shifted pattern 1021 remains under the protection of a high vacuum or inert atmosphere, preventing the adsorption of atmospheric pollutants and ensuring the purity of the oxide layer 600 growth interface. Simultaneously, it eliminates the time overhead of repeated vacuuming, breaking the vacuum, and inter-chamber transfer, significantly shortening the overall process cycle and improving equipment utilization and production efficiency.

[0066] like Figure 1 and Figure 7 As shown, where, Figure 7 This is a cross-sectional schematic diagram of removing the photoresist protective layer 400 in a correction method provided in an embodiment of the present invention. In step S14, the photoresist protective layer 400 is removed by a composite acid-free cleaning method, wherein the composite acid-free cleaning method is chemically inert to the oxide layer 600.

[0067] This step employs a composite acid-free system to replace traditional strong acid immersion or strong alkali stripping processes, fundamentally eliminating the potential corrosion risk posed by highly corrosive liquids to the phase-shift pattern 1021. The large amount of heat and intense chemical corrosion generated during traditional acid washing processes can easily lead to the collapse of fine lines or uneven thinning of the phase-shift layer 102. The composite acid-free cleaning achieves efficient expansion and stripping of the photoresist through a gentle resist removal method, significantly improving the microstructure quality of the phase-shift mask 100 surface. It effectively avoids the formation of surface micro-pits or roughness deterioration often caused by strong chemical cleaning, ensuring that the thinned phase-shift pattern 1021 surface remains highly smooth and free of visible defects. This not only guarantees the optical performance of subsequent exposure processes but also significantly extends the service life of the phase-shift mask 100, achieving a dual guarantee of process safety and pattern quality.

[0068] Because the oxide layer 600 formed in the preceding steps is extremely thin, typically only nanometer-thick, and its composition makes it highly sensitive to specific acidic and alkaline environments, if the cleaning solution is not chemically inert, it will indiscriminately etch or dissolve this oxide barrier, not only destroying its protective function but also directly causing a change in the effective refractive index of the phase-shift pattern 1021 surface, resulting in a drift or even failure of the phase shift that had been corrected to the target value. A chemically inert cleaning solution can act like a transparent protective shield, undergoing a physical stripping reaction only at the interface between the photoresist and the liquid, without producing any chemical effect on the underlying oxide layer 600 and phase-shift layer 102.

[0069] In some embodiments, the step of removing the photoresist protective layer 400 using a composite acid-free cleaning method further includes: Ultraviolet light is used to irradiate the photoresist to initiate a photolysis reaction.

[0070] Ultraviolet (UV) irradiation involves using a UV light source of a specific wavelength (typically 200-400 nm) to irradiate the surface of a phase-shifting mask 100 covered with a photoresist protective layer 400. Upon absorbing UV photon energy, the photosensitive groups in the photoresist material undergo photolysis, resulting in the breakage of the polymer backbone or side chains. This leads to a significant reduction in the molecular weight of the photoresist and the disintegration of its cross-linked structure, transforming it from a solid film into an easily soluble oligomer or monomer state. UV light acts only on the photoresist material itself, causing no chemical or physical damage to the underlying oxide layer 600, phase-shifting pattern 1021, or substrate layer 101. Furthermore, the photolysis reaction can occur at room temperature, avoiding thermal stress problems that may arise from high-temperature processing. In addition, UV irradiation can simultaneously decompose residual organic solvents and volatile impurities in the photoresist, further purifying the mask surface environment and creating favorable conditions for subsequent dissolution steps.

[0071] After ultraviolet light irradiation, the photoresist that has been photolyzed is dissolved using tetramethylammonium hydroxide (TMAH) solution.

[0072] Tetramethylammonium hydroxide is a strong organic base whose aqueous solution has extremely high dissolving power for photoresist fragments after photolysis. It can quickly strip the photoresist from the surface of the phase-shifting mask 100 and carry it into the solution. Compared with traditional inorganic strong bases such as sodium hydroxide or potassium hydroxide, tetramethylammonium hydroxide does not contain metal ions and will not leave ionic contamination residues on the mask surface, thus effectively avoiding haze defects in subsequent photolithography processes. Simultaneously, the tetramethylammonium hydroxide solution exhibits good chemical inertness to the oxide layer 600 and the phase-shifting layer 102. Under appropriate concentration and temperature conditions, it will not erode or thin the oxide layer 600, ensuring the integrity of the previously formed chemical inert barrier. By controlling the immersion time or spray flow rate, complete removal of the photoresist can be achieved, and the dissolution process is uniform and controllable, leaving no residual photoresist at the edges of the phase-shifting pattern 1021 or the corners of the transparent area 1022.

[0073] Furthermore, in some embodiments, during or after the step of dissolving the photolyzed photoresist with tetramethylammonium hydroxide solution, megasonic ultrasonic-assisted removal of residual photoresist is employed.

[0074] Megasonic ultrasound is a high-frequency vibration-assisted cleaning technology. Its operating frequency typically ranges from 800 kHz to several megahertz, significantly higher than conventional ultrasound. Under these high-frequency conditions, the cavitation bubbles generated in the liquid are extremely small, resulting in a more gentle and uniform energy release. This allows for deep penetration into the narrow transparent areas 1022 between the phase-shift patterns 1021 and the bottom of high aspect ratio trenches, effectively removing trace amounts of photoresist residue that could not be completely dissolved due to surface tension or geometric obstruction. The assistance of megasonic ultrasound not only improves cleaning efficiency but also avoids mechanical damage or fatigue cracking that conventional ultrasound may cause to the fine patterns. This step can be applied simultaneously during the tetramethylammonium hydroxide solution treatment or used alone in the post-treatment rinsing stage. Both methods significantly improve the final cleaning quality, ensuring that the surface of the phase-shift mask 100 achieves a clean state free of photoresist residue, particles, and contaminants.

[0075] In this embodiment of the invention, a composite acid-free cleaning method is used to remove the photoresist protective layer 400. The acid-free formula does not introduce high-risk ion residues such as sulfate and ammonium ions, effectively controlling the level of ion contamination and reducing the probability of haze defects in the subsequent use of the phase shift mask 100.

[0076] Optionally, after removing the photoresist protective layer 400 using a composite acid-free cleaning method, the process further includes: performing key parameter detection on the phase shift mask; if all key parameters meet the requirements, then the phase correction of the phase shift mask 100 is completed.

[0077] This inspection step is the final quality verification stage of the entire correction process. Its purpose is to comprehensively evaluate whether the phase shift mask 100, after a series of processes including thinning, oxidation, and resist removal, has been restored to a qualified state suitable for mass production. Only when all key parameters meet the design specifications can the correction process be confirmed as successful; otherwise, the inspection results will determine whether rework or scrapping is necessary. This closed-loop quality control mechanism ensures that each repaired phase shift mask 100 possesses stable and reliable optical performance and pattern accuracy, avoiding the risk of defective products flowing into downstream photolithography processes and causing batch yield losses.

[0078] The key parameters include phase shift, critical dimensions, transmittance, and surface quality. Phase shift is the primary indicator of correction effectiveness and must be accurately measured using an optical phase detector to confirm it has returned to the target value (typically 180°±5°) to ensure the optical interference function of the phase-shift mask 100 is restored to normal. Critical dimensions refer to the linewidth or spacing of the phase-shift pattern 1021, which must be inspected using a scanning electron microscope or optical critical dimension measuring equipment to confirm that no unexpected expansion or contraction has occurred during thinning and cleaning, ensuring the linewidth control accuracy of the photolithographic pattern. Transmittance refers to the proportion of light transmitted to the exposure wavelength in the phase-shift pattern 1021 area, which must be measured using a spectrophotometer or transmittance meter to ensure it is within the design specifications (typically 5%~18%), avoiding light intensity imbalance due to abnormal transmittance that could affect the interference effect. Surface quality encompasses the flatness, roughness, presence of scratches, particulate contamination, or residues on the surface of the phase-shift pattern 1021 and the substrate layer 101. A comprehensive evaluation using atomic force microscopy, optical microscopy, or dark-field defect detection equipment is required to ensure the mask surface meets a clean standard free of defects and contamination. These four parameters are interrelated and indispensable, collectively forming a complete evaluation system for the quality of the phase-shift mask 100 correction.

[0079] The phase correction method for phase-shifting masks provided in this invention effectively avoids substrate damage and lateral etching by using a photoresist protective layer to shield the substrate layer and combining it with plasma anisotropic etching, thus maintaining the critical dimensions intact. At the same time, a closed-loop dynamic feedback system is constructed to achieve precise control of the thinning amount, and an oxide layer is formed on the surface of the phase-shifting pattern after etching as a chemical inert barrier, so that subsequent composite acid-free cleaning does not erode the phase-shifting layer and the substrate layer. Ultimately, high-precision, non-destructive repair of phase-shifting masks that exceed the standard is achieved.

[0080] It should be noted that references to "an embodiment," "an embodiment," "an exemplary embodiment," "some embodiments," etc., in the specification indicate that the described embodiments may include specific features, structures, or characteristics, but each embodiment may not necessarily include that specific feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. In addition, when a specific feature, structure, or characteristic is described in connection with an embodiment, whether explicitly described or not, implementing such a feature, structure, or characteristic in conjunction with other embodiments is within the knowledge of those skilled in the art.

[0081] It should be noted that the terms "comprising" and "having," and their variations, used in this invention document are intended to cover non-exclusive inclusion. The terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence, unless explicitly indicated by the context. It should be understood that such data used interchangeably where appropriate. Furthermore, embodiments and features within embodiments of this invention can be combined with each other unless otherwise specified. In addition, descriptions of well-known components and technologies have been omitted in the above description to avoid unnecessarily obscuring the concepts of this invention. In the various embodiments described above, each embodiment focuses on its differences from other embodiments; similar or identical parts between embodiments can be referred to interchangeably.

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for correcting the phase of a phase-shifting mask, characterized in that, Includes the following steps: A phase shift mask to be corrected is provided, the phase shift mask including a base layer and a phase shift layer disposed on the base layer, the phase shift layer including a phase shift pattern, a light-transmitting area between adjacent phase shift patterns, the light-transmitting area exposing the base layer, and the phase shift mask having a phase offset greater than a predetermined value; A photoresist protective layer is formed on the phase-shifting mask, the photoresist protective layer fills the light-transmitting area, and the upper surface of the photoresist protective layer is higher than the upper surface of the phase-shifting layer; The phase shift pattern is thinned by plasma anisotropic etching, and the phase shift mask after thinning is measured. If the phase shift does not meet the requirements, plasma anisotropic etching and phase shift measurement are repeated until the phase shift of the phase shift mask meets the requirements. An oxide layer is formed on the thinned surface of the phase shift pattern; The photoresist protective layer is removed using a composite acid-free cleaning method, which is chemically inert to the oxide layer.

2. The method for correcting the phase of a phase-shifting mask according to claim 1, characterized in that, The step of forming a photoresist protective layer on the phase-shifting mask further includes the following steps: obtaining the etching selectivity ratio of the plasma anisotropic etching process for the phase-shifting pattern and the photoresist protective layer; the step of forming a photoresist protective layer on the phase-shifting mask further includes: determining the height of the photoresist protective layer based on the etching selectivity ratio and the expected thinning amount of the phase-shifting pattern.

3. The method for correcting the phase of a phase-shifting mask according to claim 1, characterized in that, The step of forming a photoresist protective layer on the phase-shifting mask further includes: A photoresist material layer is formed on the phase-shifting mask, the photoresist material layer filling the light-transmitting area and covering the upper surface of the phase-shifting pattern; The photoresist material layer is subjected to reverse polarity exposure and a development process to remove the photoresist material layer on the upper surface of the phase-shifted pattern. The remaining photoresist material layer in the light-transmitting area serves as the photoresist protective layer.

4. The method for correcting the phase of a phase-shifting mask according to claim 1, characterized in that, In the step of thinning the phase shift pattern using plasma anisotropic etching, the plasma etching direction is perpendicular to the surface of the phase shift pattern.

5. The method for correcting the phase of a phase-shifting mask according to claim 1, characterized in that, In the step of thinning the phase shift pattern using plasma anisotropic etching, the etching gas is either a chlorine-containing gas or oxygen.

6. The method for correcting the phase of a phase-shifting mask according to claim 1, characterized in that, The step of measuring the phase shift of the thinned phase shift mask further includes: performing an in-situ measurement of the phase shift in the thinned phase shift mask in a chamber for performing plasma anisotropic etching.

7. The method for correcting the phase of a phase-shifting mask according to claim 1, characterized in that, The step of measuring the phase shift of the thinned phase shift mask further includes: removing the thinned phase shift mask out of the chamber where plasma anisotropic etching is performed, and measuring its phase shift offline.

8. The method for correcting the phase of a phase-shifting mask according to claim 1, characterized in that, The step of thinning the phase shift pattern using plasma anisotropic etching and measuring the phase shift mask after thinning further includes: calculating the required plasma anisotropic etching time or etching amount for the next round based on the difference between the current phase shift and the target value, combined with the pre-calibrated correspondence between etching rate and phase change, then performing plasma anisotropic etching again, and re-measuring the phase shift after etching is completed.

9. The method for correcting the phase of a phase-shifting mask according to claim 1, characterized in that, The step of forming an oxide layer on the thinned phase-shift patterned surface further includes: forming the oxide layer in a chamber for performing plasma anisotropic etching or in a vacuum chamber connected to the chamber for performing plasma anisotropic etching.

10. The method for correcting the phase of a phase-shifting mask according to claim 1, characterized in that, The step of forming an oxide layer on the thinned phase-shift pattern surface further includes: treating the thinned phase-shift pattern surface with oxygen plasma to form the oxide layer.

11. The method for correcting the phase of a phase-shifting mask according to claim 1, characterized in that, The step of removing the photoresist protective layer using a composite acid-free cleaning method further includes: Ultraviolet light irradiation is used to initiate the photolysis reaction of the photoresist; The photoresist that has been photolyzed was dissolved using a tetramethylammonium hydroxide solution.

12. The method for correcting the phase of a phase-shifting mask according to claim 11, characterized in that, During or after the step of dissolving the photoresist that has been photolyzed with tetramethylammonium hydroxide solution, megasonic ultrasonic-assisted removal of residual photoresist is used.

13. The method for correcting the phase of a phase-shifting mask according to claim 1, characterized in that, After removing the photoresist protective layer using a composite acid-free cleaning method, the process further includes: performing key parameter detection on the phase shift mask; if all key parameters meet the requirements, then the phase correction of the phase shift mask is completed.

14. The method for correcting the phase of a phase-shifting mask according to claim 13, characterized in that, The key parameters include phase offset, key dimensions, transmittance, and surface quality.

15. The method for correcting the phase of a phase-shifting mask according to claim 1, characterized in that, The step of providing a phase-shifting mask to be corrected further includes: the phase-shifting mask further includes a light-shielding layer disposed in the substrate layer or in a region of the phase-shifting layer where light is not required to pass through; the step of forming a photoresist protective layer on the phase-shifting mask further includes: the photoresist protective layer is also formed on the light-shielding layer.

Images