Total reflection binary photomask and pattern transfer method
Through the total reflection binary optic mask structure, the optical layer and prism design are used to solve the problem of pattern accuracy and etching uneven caused by multi-layer film stacking, and high-precision and high-contrast optical pattern transfer is achieved.
Patent Information
- Application Number
- CN202510916368.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-03
- Publication Date
- 2025-08-12
AI Technical Summary
During the pattern transfer process, the existing photomasks have problems of reducing pattern accuracy and uneven etching due to the multi-layer film stacking structure, and the traditional photomasks have problems of penetrating light.
The total reflection binary optical mask structure is adopted, including a transparent substrate and an optical layer. The pattern is processed on the optical layer through the etching process, and the design of the incoming and outgoing prisms is used to ensure that the light source is incident at a certain angle and total reflection occurs, avoiding light penetration, and the gap is filled with the liquid film layer to ensure linear propagation of light.
Improves pattern clarity and etch uniformity, ensures optical contrast, and achieves higher pattern accuracy and production convenience.
Smart Images
Figure CN120469145A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of semiconductor product preparation, and in particular provides a total reflection binary mask and a pattern transfer method. Background Art
[0002] A photomask is a pattern transfer tool or master used in the microelectronics manufacturing process. It carries intellectual property information, including graphic designs and process technologies. A photomask consists of a substrate and a non-transparent layer formed on the substrate. A photomask with a light-transmitting pattern imprinted on the non-transparent layer is also called a photomask. This pattern is then transferred to a semiconductor wafer using light from a photolithography system. As semiconductor device feature sizes decrease, the corresponding circuit patterns on the photomask also become smaller and more complex. Therefore, substrate quality has become one of the most critical factors in establishing a robust and reliable semiconductor manufacturing process.
[0003] The non-transparent layer deposited on the substrate by conventional photomasks is typically a chromium-based film, produced through techniques such as sputtering or vacuum evaporation. Because chromium-based films have a high surface reflectivity, photomasks with only a single layer of chromium-based film are prone to repeated reflections during the pattern transfer process, resulting in reduced pattern accuracy on the wafer. Therefore, conventional non-transparent layers employ a stacked structure of multiple films, including anti-reflective films and light-shielding films.
[0004] However, although the multi-layer film stack structure can reduce the back-and-forth reflection between the mask and the wafer to a certain extent, the need for these multi-layer films has led to problems such as film layer design and process complexity. In addition, as the overall film thickness increases, in order to have enough time to etch the multi-layer film to produce the pattern, the thickness of the photoresist needs to increase (for example, the photoresist film thickness is required to be three times the thickness of the non-transparent film containing Cr). The increase in film thickness will cause problems such as shield collapse in node technologies with reduced line widths. In addition, when conventional photolithography technology etches and patterns the blank mask of the multi-layer stack structure, the etching rate of each film in the non-transparent layer is different, and the etching rate varies greatly in the middle of the film layer, which can easily make the etching of the entire film layer uneven, thereby affecting the clarity of the pattern.
[0005] Therefore, there is an urgent need for a photomask that is robust and reliable in quality, easy to produce, and has higher pattern definition. Summary of the Invention
[0006] In order to solve the above problems, the present invention provides a mask that is easy to produce and has higher pattern definition, and a method for transferring a pattern using the mask.
[0007] The technical solutions of the present invention are as follows:
[0008] A total reflection binary light mask includes a transparent substrate, an optical layer is provided on one side of the transparent substrate, and a light incident prism is attached to the other side. The optical layer is processed with an optical pattern through an etching process. The light receiving surface of the light incident prism is perpendicular to the direction of the light source, and enables the light source to be transmitted to the optical layer at an incident angle of α. The optical layer can cause incident light with an incident angle of α to undergo total reflection.
[0009] Different from the traditional multi-layer stacked structure of the mask, the present invention only needs to set up one optical layer and only etches this optical layer, which can effectively ensure the uniformity and accuracy of the etched pattern; and in the existing technology, the traditional binary mask still has 0.1% of penetrating light in the non-transmitting part. The present invention eliminates the penetrating light through the total reflection of the optical layer, thereby ensuring the optical contrast of the mask when in use; the light source is projected onto the optical layer at a certain angle, and compared with the traditional light source that irradiates the optical layer vertically, when transferring the pattern information, the pattern on the optical layer can be engraved onto the wafer in a reduced form, which is of great significance.
[0010] On the other hand, since it is almost impossible to ensure that the light source output from the transparent substrate does not undergo total reflection with the external medium, a first liquid film layer and a light-emitting prism are also provided on the side of the transparent substrate where the optical layer is provided. The light-emitting prism is attached to the optical layer through the first liquid film layer, and the light-emitting surface of the light-emitting prism is parallel to the light-entering surface of the light-entering prism.
[0011] In this solution, the first liquid film layer can ensure that the light-emitting prism is attached to the optical layer without any gaps, and the light-emitting prism can ensure the refractive index of the light-incident prism, so that the output light of the transparent substrate can be transmitted to the light-incident prism. The angle of the light source is changed by the light-incident prism, and ultimately the output light source will not be totally reflected even if it is output into a vacuum environment or an atmospheric environment, ensuring that the light source can be output outward from the area where the pattern is etched on the optical layer.
[0012] On the other hand, due to process or other reasons, the surface of the light-entering prism and the surface of the transparent substrate may not be completely aligned, and some air may be present. At certain angles, total internal reflection may occur, preventing the light source from fully entering the transparent substrate, thereby causing loss of the pattern. To this end, a second liquid film layer is further provided between the light-entering prism and the transparent substrate. The refractive index of the first and second liquid film layers is the same as that of the light-entering prism or the transparent substrate.
[0013] In this solution, the second liquid film layer is arranged between the light incident prism and the transparent substrate, which can completely fill and eliminate the gap between the two, ensuring that the light source can completely enter the transparent substrate.
[0014] Preferably, the refractive index of the light-emitting prism is the same as the refractive index of the light-incident prism.
[0015] In this solution, since the light-emitting surface of the light-emitting prism is parallel to the light-entering surface of the light-entering prism and their refractive indices are the same, no matter how the light is refracted between the two, the angles of the incident light and the outgoing light can be guaranteed to be the same, which makes it easier to adjust the placement angle of the wafer end and ensure the accuracy of the pattern on the wafer.
[0016] Preferably, the refractive index of the light incident prism is the same as the refractive index of the transparent substrate.
[0017] In this scheme, the refractive index of all parts of the total reflection binary mask except the optical layer is made the same, so that the light source can propagate in a straight line. By ensuring that the incident angle α is appropriate, unnecessary total reflection can be eliminated, making the light source propagation more precise and the angle easier to control.
[0018] Preferably, the incident angle α needs to satisfy:
[0019] α>arcsin(n3 / n2)
[0020] Where n2 is the refractive index of the transparent substrate, and n3 is the refractive index of the optical layer.
[0021] Preferably, the optical layer is deposited on the transparent substrate, and the refractive index of the deposited optical layer is smaller than the refractive index of the transparent substrate. Preferably, the deposited optical layer is SiN.
[0022] Since the transparent substrate used as the photomask substrate is often a highly transparent quartz substrate, the refractive index of the optical layer must be smaller than that of the highly transparent quartz substrate in order to achieve the total reflection incident angle α. The refractive index of SiN meets the requirements and the deposition steps are simple, which is conducive to production and manufacturing.
[0023] Preferably, the deposition thickness of the optical layer is 10 nm to 50 nm. A thickness greater than 50 nm will affect light sources at certain angles, while a thickness less than 10 nm is prone to penetrating light.
[0024] A pattern transfer method, using any of the above-mentioned total reflection binary mask, includes using a photolithography machine to transfer the pattern on the optical layer to a wafer, the exposure light output by the photolithography machine is vertically irradiated on the light input prism, and the wafer surface is perpendicular to the light source output by the total reflection binary mask.
[0025] Preferably, the wafer is placed horizontally, and the precise transmission of light can be ensured by simply ensuring the placement angle of the total reflection binary mask.
[0026] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:
[0027] 1. The present invention only requires one optical layer to be provided and only this optical layer to be etched, which can effectively ensure the uniformity and accuracy of the etching pattern.
[0028] 2. The present invention eliminates penetrating light through total reflection of the optical layer, ensures the optical contrast of the mask when in use, and effectively improves the clarity of the pattern.
[0029] 3. The light source of the present invention illuminates the optical layer at a certain angle. Compared with the traditional light source that illuminates the optical layer vertically, when transferring pattern information, the pattern on the optical layer can be recorded on the wafer in a reduced form, which has significant cross-generational significance. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an undue limitation of the present invention. Obviously, the drawings described below are only some embodiments. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without inventive effort. In the accompanying drawings:
[0031] Figure 1 Schematic diagram of a total reflection mask related to the present invention.
[0032] In the above drawings, the corresponding reference numerals are as follows:
[0033] 1-transparent substrate, 2-optical layer, 3-light input prism, 4-light output prism, 5-first liquid film layer, 6-second liquid film layer, 7-wafer.
[0034] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but rather to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION
[0035] In conjunction with the accompanying drawings, the technical solution of the present invention is clearly and completely described through the specific implementation methods of the embodiments of the present invention.
[0036] Example 1:
[0037] A total reflection binary mask, such as Figure 1 As shown, it includes a transparent substrate 1, characterized in that an optical layer 2 is deposited on one side of the transparent substrate 1 and a light incident prism 3 is attached to the other side, the optical layer 2 is processed with an optical pattern by an etching process, the light receiving surface of the light incident prism 3 is perpendicular to the direction of the light source, and the light source can be transmitted to the optical layer 2 at an incident angle of α, and the optical layer 2 can cause the incident light with an incident angle of α to undergo total reflection.
[0038] Specifically, since it is almost impossible to ensure that the light source output from the transparent substrate 1 will not be totally reflected by the external medium, a first liquid film layer 5 and a light-emitting prism 4 are also provided on the side of the transparent substrate 1 provided with the optical layer 2. The first liquid film layer 5 is provided on the transparent substrate 1 by spin coating, and the light-emitting prism 4 is attached to the optical layer 2 through the first liquid film layer 5. The light-emitting surface of the light-emitting prism 4 is parallel to the light-entering surface of the light-entering prism 3. The first liquid film layer 5 can ensure that the light-emitting prism 4 is attached to the optical layer 2 without any gaps, and the light-emitting prism 4 can ensure the refractive index of the light-entering prism 3. Then, the output light of the transparent substrate 1 can be transmitted to the light-entering prism 3. The angle of the light source is changed by the light-entering prism 3, and ultimately, the output light source will not be totally reflected even if it is output into a vacuum environment or an atmospheric environment, ensuring that the light source can be output outward from the area where the pattern is etched on the optical layer 2. A second liquid film layer 6 is further provided between the incident prism 3 and the transparent substrate 1. The refractive index of the first liquid film layer 5 and the second liquid film layer 6 is the same as that of the incident prism 3 or the transparent substrate 1. By providing the second liquid film layer 6 between the incident prism 3 and the transparent substrate, the gap between the two can be completely filled and eliminated, ensuring that the light source can fully enter the transparent substrate 1.
[0039] Furthermore, the refractive index of the light-emitting prism 4 is the same as the refractive index of the light-entering prism 3. Since the light-emitting surface of the light-emitting prism 4 is parallel to the light-entering surface of the light-entering prism 3 and the refractive indexes of the two are the same, no matter how the light is refracted between the two, the angles of the incident light and the outgoing light can be kept the same, which makes it easier to adjust the placement angle of the wafer 7 end and ensure the accuracy of the pattern on the wafer 7. Figure 1 As shown, if the optical layer 2 is ignored, the light input prism 3 and the light output prism 4 can be centrally symmetrically arranged on both sides of the transparent substrate 1 .
[0040] Furthermore, the refractive index of the incident prism 3 is the same as that of the transparent substrate 1. By making the refractive index of each part of the total reflection binary mask the same, the light source can propagate in a straight line within it, ensuring that the incident angle α is appropriate. This can prevent unnecessary total reflection, make the light source propagation more precise, and make the angle easier to control.
[0041] It should be noted that the deposition thickness of the optical layer 2 is 10nm to 50nm. A thickness greater than 50nm will affect the light source at a certain angle, and a thickness less than 10nm is prone to penetrating light; and the incident angle α needs to meet the following requirements:
[0042] α>arcsin(n3 / n2);
[0043] Wherein, n2 is the refractive index of the transparent substrate 1 , and n3 is the refractive index of the optical layer 2 .
[0044] This embodiment finally Figure 1As shown, the light source can directly illuminate the light incident surface of the light incident prism 3 vertically without refraction. The light passes through the second liquid film layer 6, the transparent substrate 1 and the optical layer 2 in a straight line in sequence. The light is totally reflected in the place where the optical layer 2 is not etched. The etched pattern area is filled with the first liquid film layer 5, and the light will not be refracted. It still propagates in a straight line to the light output prism 4. Since the light propagating from the light output prism 4 to the outside world is also perpendicular to the light output surface of the light output prism 4, the light output from the entire mask is a straight line.
[0045] Example 2:
[0046] This embodiment provides several detailed implementation methods based on the first embodiment.
[0047] Transparent substrate 1 is a highly transparent quartz substrate. Optical layer 2 is deposited on one side of transparent substrate 1 using Si as a target. The refractive index of optical layer 2 must be lower than that of the highly transparent quartz substrate to achieve total internal reflection at an incident angle α. The refractive index of SiN (1.303 under a 193nm wavelength light source) meets this requirement, and the deposition process is simple. The desired pattern is etched onto optical layer 2 through an etching process.
[0048] Of course, the optical layer 2 also includes but is not limited to SiO2, Al2O3, GeO2, SiO, AION, SION, MgO, MgAl2O4, MgF2, BaF2, CaF2, DyF3, YDF3, YF3 and CeF3, etc. The refractive index of these materials under a light source with a wavelength of 193nn is 1.4, which is less than the refractive index of the high-transparent stone substrate at a wavelength of 193nm, which is 1.556.
[0049] Specifically, a 152 mm square and 6.35 mm thick 6025 quartz substrate is placed in the chamber of the sputtering system as the transparent substrate 1. By sputtering the Si target with argon and nitrogen, a SiN film with a thickness of 20 nm is directly deposited on the transparent substrate 1 as the optical layer 2. The composition of the film is then analyzed by an X-ray photoelectron spectrometer XPS K-Alpha. The optical constants (refractive index n and extinction coefficient k) of the film at multiple wavelengths are measured by a spectroscopic ellipsometer VUV-VASE Gen-II. Its Si:N atomic ratio is 2:1, so the refractive index n of the optical layer 2 at a wavelength of 193 nm is 1.3, and the extinction coefficient k is 2.255, which can be used as a total reflection binary mask blank device.
[0050] Next, using etching and / or other micromachining processes, such as those used to create a mask pattern, a portion of the optical layer 2 is etched away to produce a mask pattern. Using a spin-coating process to create a photoresist layer, a 500-nanometer-thick refractive index liquid film layer is spin-coated on both the front and back surfaces of the mask, serving as the first and second liquid film layers 5 and 6, respectively. The refractive index of the refractive index liquid film layer is selected to be the same as that of the transparent substrate 1, which is n = 1.556. Finally, two prisms made of the same material as the transparent substrate 1 are attached to the first and second liquid film layers 5 and 6, respectively, and secured with the aid of a mask housing. In this embodiment, a triangular prism is selected, with three corner angles of 90, α, and 90-α degrees, respectively. The right-angled side at angle α is attached to the liquid film layer.
[0051] Finally, by controlling the angle between the wafer 7 and the light source, or controlling the angle of the total reflection mask, the exposure light emitted by the light source is vertically directed toward the incident surface of the total reflection mask and output vertically to the wafer 7 without refraction.
[0052] Different from the traditional multi-layer stacked structure of the mask, the present invention only needs to set up one optical layer 2 and only etches this optical layer 2, which can effectively ensure the uniformity and accuracy of the etching pattern; and in the existing technology, the non-transmissive part of the traditional binary mask still has 0.1% of penetrating light. The present invention eliminates the penetrating light through the total reflection of the optical layer 2, thereby ensuring the optical contrast of the mask when in use; the light source is projected onto the optical layer 2 at a certain angle. Compared with the traditional light source that irradiates the optical layer 2 vertically, when transferring the pattern information, since the light is obliquely incident on the optical layer 2, the pattern on the optical layer 2 can be reduced by COS (α) times and engraved onto the wafer 7, which is of great significance.
[0053] Example 3:
[0054] A pattern transfer method, using any of the above-mentioned total reflection binary mask, includes using a photolithography machine to transfer the pattern on the optical layer 2 to the wafer 7, the exposure light output by the photolithography machine is vertically irradiated on the light input prism 3, and the surface of the wafer 7 is perpendicular to the light source output by the total reflection binary mask.
[0055] During pattern transfer, the wafer 7 is preferably placed horizontally. At this time, the exposure light source is also vertically downward, which is easy to control. It is only necessary to ensure the placement angle of the total reflection binary mask, that is, to control the placement angle of the transparent substrate 1 to ensure accurate transmission of light.
[0056] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.
Claims
1. A total reflection binary mask, comprising a transparent substrate (1), characterized in that: An optical layer (2) is provided on one side of the transparent substrate (1), and a light incident prism (3) is attached to the other side. The optical layer (2) is processed with an optical pattern through an etching process. The light receiving surface of the light incident prism (3) is perpendicular to the direction of the light source, and enables the light source to be transmitted to the optical layer (2) at an incident angle of α. The optical layer (2) can cause incident light with an incident angle of α to undergo total reflection.
2. A total reflection binary mask according to claim 1, characterized in that A first liquid film layer (5) and a light-emitting prism (4) are also provided on one side of the transparent substrate (1) provided with the optical layer (2); the light-emitting prism (4) is attached to the optical layer (2) via the first liquid film layer (5); and the light-emitting surface of the light-emitting prism (4) is parallel to the light-entering surface of the light-entering prism (3).
3. The total reflection binary mask according to claim 2, characterized in that: A second liquid film layer (6) is further provided between the light incident prism (3) and the transparent substrate (1); the refractive index of the first liquid film layer (5) and the second liquid film layer (6) is the same as the refractive index of the light incident prism (3) or the transparent substrate (1).
4. The total reflection binary mask according to claim 3, characterized in that: The refractive index of the light-emitting prism (4) is the same as the refractive index of the light-incoming prism (3).
5. The total reflection binary mask according to claim 4, characterized in that: The refractive index of the light incident prism (3) is the same as the refractive index of the transparent substrate (1).
6. A total reflection binary mask according to any one of claims 1 to 5, characterized in that: The incident angle α needs to satisfy: α>arcsin(n3 / n2) Wherein n2 is the refractive index of the transparent substrate (1), and n3 is the refractive index of the optical layer (2).
7. The total reflection binary mask according to claim 1, characterized in that: The optical layer (2) is deposited on the transparent substrate (1), and the refractive index of the deposited optical layer (2) is smaller than the refractive index of the transparent substrate (1).
8. The total reflection binary mask according to claim 7, characterized in that: The deposition thickness of the optical layer (2) is 10 nm to 50 nm.
9. A pattern transfer method, characterized in that: Using a total reflection binary mask as described in any one of claims 1 to 8, comprising using a photolithography machine to transfer the pattern on the optical layer (2) to a wafer (7), the exposure light output by the photolithography machine is vertically irradiated on the light input prism (3), and the surface of the wafer (7) is perpendicular to the light source output by the total reflection binary mask.
10. A pattern transfer method according to claim 9, characterized in that: The wafer (7) is placed horizontally.
Citation Information
Cited By
Oblique etching method for optical layer of photomask
CN121411085A