Method for improving transmittance of photomask
The molybdenum silicide layer was etched using a chlorine-based dry etching process, which solved the problem of reduced mask transmittance and achieved an increase in mask transmittance to meet product specifications.
Patent Information
- Application Number
- CN202511047347.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-28
- Publication Date
- 2025-09-30
AI Technical Summary
In the prior art, the etching of the molybdenum silicide layer of the mask is difficult to control, resulting in over-etching of the substrate and reduced transmittance of the mask, making it difficult to meet product specification requirements.
A chlorine-based dry etching process is adopted, and the patterned photoresist layer is used as a mask to etch the molybdenum silicide layer to thin and flatten the first light-transmitting area, thereby improving the transmittance of the molybdenum silicide layer.
By thinning and flattening the MoSi layer, the transmittance of the photomask is improved to meet product specifications without changing the critical dimensions of the photomask.
Smart Images
Figure CN120722644A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of semiconductor technology, and in particular to a method for improving the transmittance of a photomask. Background Art
[0002] Currently, the dry etching of phase shift masks (PSMs) primarily involves etching the chromium (Cr) layer and the molybdenum silicide (MoSi) layer. The etching quality of the chromium layer primarily determines the critical dimension (CD) of the product, while the etching quality of the MoSi layer primarily determines the transmittance (trans) and phase difference (phase) of the product. The MoSi layer etching monitoring methods are divided into time mode and endpoint mode. The time mode uses a fixed etching time, but a fixed etching time is difficult to cover all products with a certain aperture ratio. Products with extremely low aperture ratios can over-etch the substrate. The endpoint mode stops etching at that step after the system detects the endpoint, and then continues with the next step to control the etching depth. However, there are cases where the endpoint is not detected, resulting in over-etching of the substrate. Therefore, both etching monitoring methods may cause substrate overetching, and substrate overetching will increase the substrate transmittance. The transmittance of the photomask is the ratio of the transmittance of the molybdenum silicide layer to the transmittance of the substrate. When the substrate transmittance increases while the transmittance of the molybdenum silicide layer remains roughly unchanged, the transmittance of the photomask will decrease.
[0003] After the mask is prepared and before the film is applied, the transmittance of the mask is measured. The transmittance will affect the exposure quality of the client's wafer fab lithography machine, so it is particularly important to control the transmittance of the mask to meet the specification value. With the conventional dry etching technology currently used, the transmittance of the entire mask is mainly affected by the over-etching depth of the substrate. However, the transmittance changes rapidly, making it difficult to control the transmittance. Once the substrate over-etching depth is too deep, the transmittance cannot be adjusted back to meet product requirements through conventional means. For example, it is impossible to use chemical deposition or physical deposition to repair the over-etched substrate. As a result, the transmittance of the mask will be lower than the limit or not meet the customer's specifications, affecting the quality of the mask product, and in serious cases, even causing the mask product to be scrapped.
[0004] Figures 1 to 6 This is a cross-sectional diagram of the corresponding steps in a method for preparing a photomask in the prior art. Figure 1 , providing a substrate 10, the substrate 10 includes a molybdenum silicide layer 20, a chromium layer 30 and a first photoresist layer 41 stacked sequentially from bottom to top. Figure 2, the first photoresist layer 41 is exposed and developed to obtain a first patterned photoresist layer 41a, which covers a portion of the chromium layer 30; then, the chromium layer 30 is etched using the first patterned photoresist layer 41a as a mask to expose a portion of the molybdenum silicide layer 20. Please refer to Figure 3 , remove the first patterned photoresist layer 41a; then, a dry etching process is used to etch the exposed molybdenum silicide layer 20 to expose a portion of the substrate 10. Since the etching process of the molybdenum silicide layer 20 is difficult to control, over-etching is prone to occur, and over-etching to the substrate 10 results in a depression (such as Figure 3 As shown in the dotted box), over-etching of the substrate 10 will increase the transmittance of the substrate 10. The transmittance of the substrate 10 is the transmittance of the exposed substrate 10. Figure 4 , forming a second photoresist layer 42 to cover the chrome layer 30 and the exposed substrate 10. Figure 5 , the second photoresist layer 42 is exposed and developed to obtain a second patterned photoresist layer 42a, which covers a portion of the chromium layer 30. Figure 6 The chromium layer 30 is etched using the second patterned photoresist layer 42a as a mask to expose a portion of the molybdenum silicide layer 20; then, the second patterned photoresist layer 42a is removed to complete the preparation of the photomask.
[0005] After the mask is prepared and before the film is applied, the transmittance of the mask will be measured. Since over-etching of the substrate 10 will increase the transmittance of the substrate 10, the transmittance of the substrate 10 is the transmittance of the exposed substrate 10, and the transmittance of the molybdenum silicide layer 20 is the transmittance of the exposed molybdenum silicide layer 20. The transmittance of the mask is the ratio of the transmittance of the molybdenum silicide layer 20 to the transmittance of the substrate 10. When the transmittance of the substrate 10 increases, while the transmittance of the molybdenum silicide layer 20 remains roughly unchanged, the transmittance of the mask will decrease, causing the transmittance of the mask to be lower than the limit or not meet customer specifications. Summary of the Invention
[0006] The object of the present invention is to provide a method for improving the transmittance of a photomask, which is beneficial to improving the transmittance of a molybdenum silicide layer in a first light-transmitting region, thereby improving the transmittance of the photomask to meet product specifications without changing the critical dimensions of the photomask.
[0007] In order to achieve the above object, the present invention provides a method for improving the transmittance of a mask, comprising:
[0008] A photomask is provided, comprising a substrate, a molybdenum silicide layer, and a chromium layer stacked sequentially from bottom to top, the chromium layer being located in an opaque region of the photomask, the chromium layer exposing a portion of the molybdenum silicide layer and a portion of the substrate, the exposed molybdenum silicide layer being located in a first light-transmitting region of the photomask, the exposed substrate being located in a second light-transmitting region of the photomask, and the transmittance of the photomask being lower than a specification value;
[0009] forming a patterned photoresist layer to cover the chromium layer;
[0010] Using the patterned photoresist layer as a mask, etching the molybdenum silicide layer in the first light-transmitting area using a chlorine-based dry etching process to thin and flatten the molybdenum silicide layer in the first light-transmitting area; and
[0011] The patterned photoresist layer is removed.
[0012] Optionally, the etching gas of the chlorine-based dry etching process includes chlorine and oxygen.
[0013] Optionally, the gas ratio of the chlorine gas to the oxygen gas is greater than or equal to 9:1.
[0014] Optionally, the lower electrode energy of the chlorine-based dry etching process is 10W to 12W.
[0015] Optionally, before providing the photomask, the photomask is measured to obtain the transmittance of the photomask.
[0016] Optionally, in the provided photomask, the transmittance of the molybdenum silicide layer is lower than the transmittance of the substrate.
[0017] Optionally, in the provided mask, the substrate of the second light-transmitting area is over-etched to form a pit, and the transmittance of the substrate of the second light-transmitting area is greater than the transmittance of the substrate of the first light-transmitting area and the opaque area.
[0018] Optionally, the step of forming a patterned photoresist layer to cover the chromium layer includes:
[0019] forming a photoresist layer covering the first light-transmitting area, the second light-transmitting area, and the light-impermeable area;
[0020] The photoresist layer is exposed and developed in sequence to obtain the patterned photoresist layer.
[0021] Optionally, the transmittance of the mask is a ratio of the transmittance of the molybdenum silicide layer in the first light-transmitting area to the transmittance of the substrate in the second light-transmitting area.
[0022] Optionally, after removing the patterned photoresist layer, the method further includes measuring the transmittance of the mask.
[0023] The method for improving the transmittance of a photomask provided by the present invention includes: providing a photomask, the photomask including a substrate, a molybdenum silicide layer, and a chromium layer stacked sequentially from bottom to top, the chromium layer being located in an opaque region of the photomask, the chromium layer exposing a portion of the molybdenum silicide layer and a portion of the substrate, the exposed molybdenum silicide layer being located in a first light-transmitting region of the photomask, the exposed substrate being located in a second light-transmitting region of the photomask, and the transmittance of the photomask being lower than a specification value; forming a patterned photoresist layer to cover the chromium layer; using the patterned photoresist layer as a mask, etching the molybdenum silicide layer in the first light-transmitting region using a chlorine-based dry etching process to thin and flatten the molybdenum silicide layer in the first light-transmitting region; and removing the patterned photoresist layer. The present invention uses the patterned photoresist layer as a mask to perform a chlorine-based dry etching on the molybdenum silicide layer in the first light-transmitting region, thereby thinning and flattening the molybdenum silicide layer in the first light-transmitting region, thereby improving the transmittance of the molybdenum silicide layer in the first light-transmitting region, thereby improving the transmittance of the photomask to meet product specifications without changing the critical dimensions of the photomask. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figures 1 to 6 It is a cross-sectional schematic diagram of corresponding steps in a method for preparing a photomask in the prior art.
[0025] Figure 7 A flow chart of a method for improving the transmittance of a photomask provided by one embodiment of the present invention.
[0026] Figures 8 to 11 A cross-sectional schematic diagram of corresponding steps in a method for improving the transmittance of a photomask provided by an embodiment of the present invention.
[0027] in, Figures 1 to 6 The accompanying drawings are:
[0028] 10 - substrate; 20 - molybdenum silicide layer; 30 - chromium layer; 41 - first photoresist layer; 41a - first patterned photoresist layer; 42 - second photoresist layer; 42a - second patterned photoresist layer.
[0029] Figures 8 to 11 The accompanying drawings are:
[0030] 100 - substrate; 200 - molybdenum silicide layer; 300 - chromium layer; 400 - photoresist layer; 400a - patterned photoresist layer; A1 - first light-transmitting area; A2 - second light-transmitting area; A3 - opaque area. DETAILED DESCRIPTION
[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. The drawings are all in a very simplified form and are not drawn to scale. They are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In addition, the structures shown in the drawings are often part of the actual structure; in particular, the emphasis of each drawing is different, and sometimes different scales are used.
[0032] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.
[0033] In the description of this application, it should be understood that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, or are the orientation or position relationship in which the product of the application is usually placed when in use, or are the orientation or position relationship commonly understood by those skilled in the art. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.
[0034] In addition, relational terms such as the terms "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such article or device. In the absence of further restrictions, an element defined by the statement "comprising a ..." does not exclude the presence of other identical elements in the article or device comprising the element. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.
[0035] Figure 7 This is a flow chart of a method for improving the transmittance of a photomask provided in this embodiment. Figure 7 This embodiment provides a method for improving the transmittance of a photomask, comprising:
[0036] Step S1: Providing a photomask, the photomask comprising a substrate, a molybdenum silicide layer, and a chromium layer stacked sequentially from bottom to top, the chromium layer being located in an opaque region of the photomask, the chromium layer exposing a portion of the molybdenum silicide layer and a portion of the substrate, the exposed molybdenum silicide layer being located in a first light-transmitting region of the photomask, the exposed substrate being located in a second light-transmitting region of the photomask, and the transmittance of the photomask being lower than a specification value;
[0037] Step S2: forming a patterned photoresist layer to cover the chromium layer;
[0038] Step S3: using the patterned photoresist layer as a mask, etching the molybdenum silicide layer in the first light-transmitting area by a chlorine-based dry etching process to thin and flatten the molybdenum silicide layer in the first light-transmitting area;
[0039] Step S4: removing the patterned photoresist layer.
[0040] Figures 8 to 11 This is a cross-sectional schematic diagram of the corresponding steps in a method for improving the transmittance of a photomask provided in this embodiment. Figures 8 to 11 A method for improving the transmittance of a photomask provided in this embodiment is described in detail.
[0041] Please refer to Figure 8 , perform step S1: provide a photomask, the photomask includes a substrate 100, a molybdenum silicide layer 200, and a chromium layer 300 stacked in sequence from bottom to top, the chromium layer 300 is located in the opaque area A3 of the photomask, and the chromium layer 300 exposes a portion of the molybdenum silicide layer 200 and a portion of the substrate 100. Specifically, the chromium layer 300 exposes a portion of the molybdenum silicide layer 200, and the molybdenum silicide layer 200 exposes a portion of the substrate 100. The exposed molybdenum silicide layer 300 is located in the first light-transmitting area A1 of the photomask, and the exposed substrate 100 is located in the second light-transmitting area A2 of the photomask. Before providing the photomask, the photomask is measured to obtain the transmittance of the photomask, and the transmittance of the photomask is lower than the specification value. The specification value can be a conventional value of the transmittance of the photomask or a customer specification value of the transmittance of the photomask. When the transmittance of the photomask is lower than the specification value, the quality of the photomask will be affected. Therefore, this embodiment improves the photomask whose transmittance is lower than the specification value to improve the transmittance of the photomask.
[0042] In this embodiment, in the provided mask, the substrate 100 of the second light-transmitting area A2 is over-etched to form a pit (shown in the dotted box in the figure), and the pit is formed by etching the molybdenum silicide layer 200 when preparing the mask. Since the substrate 100 of the second light-transmitting area A2 is over-etched, the transmittance of the substrate 100 of the second light-transmitting area A2 increases, and the transmittance of the substrate 100 of the second light-transmitting area A2 is greater than the transmittance of the substrate 100 of the first light-transmitting area A1 and the transmittance of the substrate 100 of the opaque area A3, and the surface of the molybdenum silicide layer 200 is relatively rough. In the provided mask, the transmittance of the molybdenum silicide layer 200 (including the first light-transmitting area A1 and the opaque area A3) is lower than the transmittance of the substrate 100 (including the first light-transmitting area A1, the second light-transmitting area A2 and the opaque area A3). The transmittance of the molybdenum silicide layer 200 is generally low, while the substrate 100 can be a transparent substrate, the material of the substrate 100 can be quartz, and the transmittance of the substrate 100 is relatively high.
[0043] In this embodiment, the transmittance of the mask is the ratio of the transmittance of the molybdenum silicide layer 200 in the first light-transmitting area A1 to the transmittance of the substrate 100 in the second light-transmitting area A2. Since the transmittance of the substrate 100 in the second light-transmitting area A2 increases, while the transmittance of the molybdenum silicide layer 200 in the first light-transmitting area A1 remains roughly unchanged, the transmittance of the mask decreases. Therefore, in this embodiment, the transmittance of the mask is improved by increasing the transmittance of the molybdenum silicide layer 200 in the first light-transmitting area A1.
[0044] Please refer to Figure 8 and Figure 9 , performing step S2: forming a patterned photoresist layer 400a to cover the chromium layer 300. Specifically, the photoresist layer 400 is formed to cover the first light-transmitting area A1, the second light-transmitting area A2, and the opaque area A3 (i.e., covering the entire photomask); then, sequentially exposing and developing the photoresist layer 400 to obtain a patterned photoresist layer 400a. The patterned photoresist layer 400a is used to protect the chromium layer 300 from being affected by subsequent dry etching. The exposure and development preparation process for forming the patterned photoresist layer 400a is a common method and will not be described in detail here. After the patterned photoresist layer 400a is formed, the molybdenum silicide layer 200 in the first light-transmitting area A1 and the substrate 100 in the second light-transmitting area A2 are exposed, wherein the molybdenum silicide layer 200 in the first light-transmitting area A1 has a first thickness h1.
[0045] Furthermore, before forming the photoresist layer 400, the surface of the photomask is cleaned to remove residual particles on the surface to prevent the quality of the photomask from being affected in subsequent processes. After development, the surface of the photomask is cleaned to remove development byproducts or environmental particles to prevent the quality of the photomask from being affected in subsequent processes.
[0046] Please refer to Figure 10, executing step S3: using the patterned photoresist layer 400a as a mask, etching the molybdenum silicide layer 200 in the first light-transmitting area A1 using a chlorine-based dry etching process to thin and planarize the molybdenum silicide layer 200 in the first light-transmitting area A1. In this embodiment, by using a specially adjusted dry etching gas ratio and lower electrode energy, it is possible to planarize the surface of the molybdenum silicide layer 200 in the first light-transmitting area A1 and thin the molybdenum silicide layer 200 in the first light-transmitting area A1 without affecting the etching of the chromium layer 300 and the substrate 100 in the second light-transmitting area A2, nor affecting the critical dimension (CD) of the mask. In this embodiment, the chlorine-based dry etching process is performed in an etching chamber. The etching gas of the chlorine-based dry etching process includes chlorine and oxygen, and the gas ratio of chlorine to oxygen is greater than or equal to 9:1. The lower electrode energy of the chlorine-based dry etching process (the lower electrode energy of the etching chamber) is 10W to 12W. Under conventional dry etching gas ratios, the oxygen gas ratio is generally high, which can affect the chromium layer 300 beneath the patterned photoresist layer 400a during etching, resulting in defects in the chromium layer 300. Therefore, the present embodiment has developed an optimal dry etching gas ratio, namely, a chlorine to oxygen gas ratio greater than or equal to 9:1, which prevents defects in the chromium layer 300. However, the increased chlorine gas ratio can lead to excessively rapid etching of the molybdenum silicide layer 200, making it more difficult to control the transmittance to the specified value. Therefore, the present embodiment has developed an optimal dry etching bottom electrode energy, namely, a chlorine-based dry etching process bottom electrode energy of 10W to 12W. At this bottom electrode energy, the etching rate of the molybdenum silicide layer 200 is effectively controlled, and the etching chamber environment is stable. In this embodiment, the total thickness of the molybdenum silicide layer 200 thinned and flattened in the first light-transmitting area A1 is related to the over-etching depth (depression depth) of the substrate 100 in the second light-transmitting area A2. Preferably, the ratio of the total thickness of the molybdenum silicide layer 200 thinned and flattened in the first light-transmitting area A1 to the over-etching depth of the substrate 100 in the second light-transmitting area A2 is 1:5 to 1:8. For example, when the over-etching depth of the substrate 100 in the second light-transmitting area A2 is 4 nm to 5 nm, the total thickness of the molybdenum silicide layer 200 thinned and flattened in the first light-transmitting area A1 is 0.5 nm to 1 nm.
[0047] After adopting the specially adjusted dry etching gas ratio and lower electrode energy in this embodiment, the molybdenum silicide layer 200 in the first light-transmitting area A1 is thinned and flattened. The molybdenum silicide layer 200 in the first light-transmitting area A1 has a second thickness h2 (h2 is less than h1), and the chlorine-based dry etching process will not have an etching effect on the chromium layer 300 and the substrate 100 in the second light-transmitting area A2, nor will it affect the critical dimensions of the mask; thinning and flattening the molybdenum silicide layer 200 in the first light-transmitting area A1 can improve the transmittance of the molybdenum silicide layer 200 in the first light-transmitting area A1, thereby improving the transmittance of the mask.
[0048] Please refer to Figure 11 , proceed to step S4: remove the patterned photoresist layer 400a; and clean the surface of the mask. After removing the patterned photoresist layer 400a, measure the transmittance of the mask to confirm whether it meets the specification. If the transmittance of the mask is still less than the specification, repeat steps S2 and S3 to increase the transmittance of the mask to meet the specification. Increasing the transmittance of the mask will slightly reduce the phase of the mask without changing the critical dimension of the mask.
[0049] In summary, the method for improving the transmittance of a photomask provided by the present invention includes: providing a photomask, the photomask including a substrate, a molybdenum silicide layer, and a chromium layer stacked sequentially from bottom to top, the chromium layer being located in an opaque region of the photomask, the chromium layer exposing a portion of the molybdenum silicide layer and a portion of the substrate, the exposed molybdenum silicide layer being located in a first light-transmitting region of the photomask, the exposed substrate being located in a second light-transmitting region of the photomask, and the transmittance of the photomask being lower than a specification value; forming a patterned photoresist layer to cover the chromium layer; using the patterned photoresist layer as a mask, etching the molybdenum silicide layer in the first light-transmitting region using a chlorine-based dry etching process to thin and flatten the molybdenum silicide layer in the first light-transmitting region; and removing the patterned photoresist layer. The present invention utilizes the patterned photoresist layer as a mask to perform chlorine-based dry etching on the molybdenum silicide layer in the first light-transmitting region, thereby thinning and flattening the molybdenum silicide layer in the first light-transmitting region, thereby improving the transmittance of the molybdenum silicide layer in the first light-transmitting region, thereby improving the transmittance of the photomask to meet product specifications without changing the critical dimensions of the photomask.
[0050] The above description is merely a preferred embodiment of the present invention and does not limit the present invention in any way. Any person skilled in the art who, without departing from the scope of the present invention, makes any equivalent substitution, modification, or other changes to the technical solution and technical content disclosed in the present invention shall be deemed to be within the scope of the present invention and still fall within the scope of protection of the present invention.
Claims
1. A method for improving the transmittance of a photomask, characterized in that: include: A photomask is provided, comprising a substrate, a molybdenum silicide layer, and a chromium layer stacked sequentially from bottom to top, the chromium layer being located in an opaque region of the photomask, the chromium layer exposing a portion of the molybdenum silicide layer and a portion of the substrate, the exposed molybdenum silicide layer being located in a first light-transmitting region of the photomask, the exposed substrate being located in a second light-transmitting region of the photomask, and the transmittance of the photomask being lower than a specification value; forming a patterned photoresist layer to cover the chromium layer; Using the patterned photoresist layer as a mask, etching the molybdenum silicide layer in the first light-transmitting area using a chlorine-based dry etching process to thin and flatten the molybdenum silicide layer in the first light-transmitting area; and The patterned photoresist layer is removed.
2. The method for improving the transmittance of a photomask according to claim 1, wherein: The etching gas of the chlorine-based dry etching process includes chlorine and oxygen.
3. The method for improving the transmittance of a photomask according to claim 2, wherein: The gas ratio of the chlorine gas to the oxygen gas is greater than or equal to 9:
1.
4. The method for improving the transmittance of a photomask according to claim 2 or 3, wherein: The energy of the lower electrode in the chlorine-based dry etching process is 10W to 12W.
5. The method for improving the transmittance of a photomask according to claim 1, wherein: Before providing the photomask, the photomask is measured to obtain the transmittance of the photomask.
6. The method for improving the transmittance of a photomask according to claim 1, wherein: In the provided photomask, the transmittance of the molybdenum silicide layer is lower than the transmittance of the substrate.
7. The method for improving the transmittance of a photomask according to claim 1, wherein: In the provided photomask, a base of the second light-transmitting area is over-etched to form a pit, and a transmittance of the base of the second light-transmitting area is greater than a transmittance of the base of the first light-transmitting area and the opaque area.
8. The method for improving the transmittance of a photomask according to claim 1, wherein: The step of forming a patterned photoresist layer to cover the chromium layer comprises: forming a photoresist layer covering the first light-transmitting area, the second light-transmitting area, and the light-impermeable area; The photoresist layer is exposed and developed in sequence to obtain the patterned photoresist layer.
9. The method for improving the transmittance of a photomask according to claim 1, wherein: The transmittance of the mask is a ratio of the transmittance of the molybdenum silicide layer in the first light-transmitting area to the transmittance of the substrate in the second light-transmitting area.
10. The method for improving the transmittance of a photomask according to claim 1, wherein: After removing the patterned photoresist layer, the method further includes measuring the transmittance of the mask.