Inspection system including side illumination unit and inspection method using the same

Abstract

The inspection system includes a stage unit on which a blank mask is loaded. A side illumination unit having a plurality of LEDs is provided, positioned opposite to the side of the blank mask. A camera is provided positioned adjacent to the blank mask. An inspection beam irradiated from the side illumination unit toward the side of the blank mask may be substantially parallel to the upper surface of the blank mask.

Description

Technology Field

[0001] This invention relates to a blank mask inspection system and inspection method having a side lighting unit. Background Technology

[0002] Various types of masks are used in the manufacturing process of semiconductor devices. These masks are formed using blank masks. Defects in the blank masks cause various problems in the semiconductor device manufacturing process. Therefore, a technology capable of rapidly and accurately inspecting defects in the blank masks is required. The problem to be solved

[0003] The objective according to embodiments of the technical concept of the present invention is to provide an inspection system and an inspection method capable of rapidly and accurately inspecting defects in a blank mask. means of solving the problem

[0004] An inspection system according to embodiments of the technical concept of the present invention includes a stage unit on which a blank mask is loaded. A side illumination unit having a plurality of LEDs is provided, positioned opposite to the side of the blank mask. A camera is provided positioned adjacent to the blank mask.

[0005] An inspection method according to embodiments of the technical concept of the present invention includes loading a blank mask onto a stage unit. An inspection beam emitted from a side lighting unit is irradiated onto the blank mask. An image of the blank mask is detected using a camera.

[0006] An inspection system according to embodiments of the technical concept of the present invention includes a stage unit on which a blank mask is loaded. An illumination unit having a plurality of LEDs is provided, disposed adjacent to the blank mask. A camera disposed adjacent to the blank mask is provided. An image processing unit connected to the camera is provided. The illumination unit includes a side illumination unit that irradiates an inspection ray forming an angle of 0 to 10 degrees with respect to the upper surface of the blank mask toward the side of the blank mask; an inclined illumination unit that irradiates an inspection ray forming an angle of 15 to 85 degrees with respect to the upper surface of the blank mask toward the upper surface of the blank mask; and a vertical illumination unit that irradiates an inspection ray forming an angle of 85 to 90 degrees with respect to the upper surface of the blank mask toward the upper surface of the blank mask. Effects of the invention

[0007] According to embodiments of the technical concept of the present invention, a side illumination unit having a plurality of LEDs is provided, which is positioned opposite to the side of a blank mask. The side illumination unit can serve to irradiate an inspection beam substantially parallel to the upper surface of the blank mask toward the side of the blank mask. By using the side illumination unit, defects on the surface, interior, corners, and chamfers of the blank mask can be effectively detected. The horizontal width of the side illumination unit may be greater than the maximum horizontal width of the blank mask. Defects in the blank mask can be detected quickly. An inspection system and an inspection method capable of inspecting defects in the blank mask quickly and accurately can be provided. Brief explanation of the drawing

[0008] FIG. 1 is a schematic diagram illustrating an inspection system according to embodiments of the technical concept of the present invention. FIG. 2 is a block diagram illustrating an inspection system according to embodiments of the technical concept of the present invention. FIGS. 3 to 8 are layouts for explaining a side illumination unit of an inspection system according to embodiments of the technical concept of the present invention. FIGS. 9 to 11 are cross-sectional views for explaining a blank mask according to embodiments of the technical concept of the present invention. FIGS. 12 to 14 are schematic diagrams for explaining an inspection system according to embodiments of the technical concept of the present invention. FIGS. 15 to 19 are schematic diagrams for explaining inspection methods using an inspection system according to embodiments of the technical concept of the present invention. Specific details for implementing the invention

[0009] FIG. 1 is a schematic diagram for explaining an inspection system (100) according to embodiments of the technical concept of the present invention.

[0010] Referring to FIG. 1, an inspection system (100) according to embodiments of the technical concept of the present invention may include a stage unit (21), an illumination unit (30), a camera (56), and an image processing unit (67). The illumination unit (30) may include a side illumination unit (31), an inclined illumination unit (42), and a vertical illumination unit (43).

[0011] A blank mask (10) may be loaded onto the stage unit (21). The blank mask (10) may have a horizontal width greater than its thickness. The stage unit (21) may be capable of performing various movement functions on the blank mask (10), such as horizontal movement, vertical movement, rotational movement, flipping movement, tilting movement, or a combination thereof.

[0012] Each of the side lighting unit (31), the inclined lighting unit (42), and the vertical lighting unit (43) may include a plurality of LEDs. Each of the side lighting unit (31), the inclined lighting unit (42), and the vertical lighting unit (43) may include a Visible Light Emitting Diode (VLED), an Infrared Emitting Diode (IRED), an Ultraviolet Light Emitting Diode (UVLED), or a combination thereof. For example, each of the side lighting unit (31), the inclined lighting unit (42), and the vertical lighting unit (43) may include a plurality of Visible Light Emitting Diodes (VLEDs). Each of the side lighting unit (31), the inclined lighting unit (42), and the vertical lighting unit (43) may be turned on or off independently. The distance between each of the side lighting unit (31), the inclined lighting unit (42), and the vertical lighting unit (43) and the blank mask (10) can be independently and organically controlled. In one embodiment, one or all of the inclined lighting unit (42) and the vertical lighting unit (43) may be omitted.

[0013] The side lighting unit (31) may be positioned adjacent to the side of the blank mask (10). The side lighting unit (31) may be positioned opposite the side of the blank mask (10). The center of the side lighting unit (31) may be aligned toward the side of the blank mask (10). The side lighting unit (31) may irradiate an inspection ray toward the side of the blank mask (10). The side lighting unit (31) may be positioned to irradiate an inspection ray substantially parallel to the upper surface of the blank mask (10).

[0014] In one embodiment, the angle formed between the inspection ray irradiated from the side lighting unit (31) and the upper surface of the blank mask (10) may be 0 degrees to 10 degrees. The side lighting unit (31) may be moved in an up-and-down direction. The side lighting unit (31) may irradiate an inspection ray toward the side of the blank mask (10). The distance between the side lighting unit (31) and the blank mask (10) may be controlled. The thickness of the side lighting unit (31) may be greater than the thickness of the blank mask (10). The thickness of the side lighting unit (31) may be less than or equal to twice the thickness of the blank mask (10).

[0015] The inclined lighting unit (42) may be spaced apart from the side lighting unit (31). The inclined lighting unit (42) may be positioned to irradiate an inspection ray in an inclined direction toward the upper surface of the blank mask (10). In one embodiment, the angle formed between the inspection ray irradiated by the inclined lighting unit (42) and the upper surface of the blank mask (10) may be 15 degrees to 85 degrees.

[0016] The vertical lighting unit (43) may be spaced apart from the inclined lighting unit (42) and the side lighting unit (31). The vertical lighting unit (43) may be positioned adjacent to the camera (56). The vertical lighting unit (43) may be positioned to irradiate an inspection ray in a direction substantially perpendicular to the upper surface of the blank mask (10). In one embodiment, the angle formed between the inspection ray irradiated from the vertical lighting unit (43) and the upper surface of the blank mask (10) may be 85 degrees to 90 degrees.

[0017] The camera (56) may be positioned adjacent to the blank mask (10). The camera (56) may be aligned at various angles with respect to the upper surface of the blank mask (10) through horizontal movement, vertical movement, tilting movement, rotational movement, or a combination thereof. In one embodiment, the camera (56) may be aligned to the center of the blank mask (10). The camera (56) may serve to detect an image of the blank mask (10).

[0018] The camera (56) may include a Charge Coupled Device (CCD), a Complementary Metal Oxide Semiconductor Image Sensor (CIS), or a combination thereof. For example, the camera (56) may include a high-resolution CCD camera. The camera (56) may be controlled in conjunction with the stage unit (21). The camera (56) may be controlled in conjunction with the stage unit (21) and the lighting unit (30).

[0019] The image processing unit (67) may be connected to the camera (56) via a wired, wireless, or a combination thereof. The image processing unit (67) may receive, process, analyze, and output an image of the blank mask (10) detected by the camera (56).

[0020] FIG. 2 is a block diagram for explaining an inspection system (100) according to embodiments of the technical concept of the present invention.

[0021] Referring to FIG. 2, an inspection system (100) according to embodiments of the technical concept of the present invention may include a stage unit (SU), an illumination unit (IU), a camera (VU), an image processing unit (IPU), a handling unit (HU), and a clean air system (CAS). The camera (VU) may be part of a high resolution vision unit.

[0022] A blank mask (10) may be loaded onto the stage unit (SU). In one embodiment, the stage unit (SU) may include the stage unit (21 in FIG. 1). The lighting unit (IU) may be positioned adjacent to the blank mask (10). The lighting unit (IU) may be moved in conjunction with the stage unit (SU) and the camera (VU). In one embodiment, the lighting unit (IU) may include the lighting unit (30 in FIG. 1).

[0023] The camera (VU) may be positioned adjacent to the stage unit (SU). The camera (VU) may be aligned toward the blank mask (10). The camera (VU) may be moved in conjunction with the stage unit (SU). In one embodiment, the camera (VU) may include the camera (56 in FIG. 1). The image processing unit (IPU) may be connected to the camera (VU) via wired, wireless, or a combination thereof. The image processing unit (IPU) may receive, process, analyze, and output an image of the blank mask (10) detected by the camera (VU). In one embodiment, the image processing unit (IPU) may include the image processing unit (67 in FIG. 1).

[0024] The handling unit (HU) may be positioned adjacent to the stage unit (SU). The handling unit (HU) may perform the function of loading and unloading the blank mask (10) to the stage unit (SU). The air purification system (CAS) may be positioned adjacent to the stage unit (SU) and the lighting unit (IU). The air purification system (CAS) may supply clean air to the stage unit (SU), the lighting unit (IU), the blank mask (10), the camera (VU), and the surroundings thereof. The air purification system (CAS) may prevent contamination of the blank mask (10) and its surroundings.

[0025] FIGS. 3 to 8 are layouts for explaining a side illumination unit (Side Illumination Unit; 31) of an inspection system according to embodiments of the technical concept of the present invention.

[0026] Referring to FIG. 3, the side lighting unit (31) may include a first side lighting unit (31A), a second side lighting unit (31B), a third side lighting unit (31C), and a fourth side lighting unit (31D). The second side lighting unit (31B) may be positioned opposite the first side lighting unit (31A). A blank mask (10) may be positioned between the first side lighting unit (31A) and the second side lighting unit (31B). The fourth side lighting unit (31D) may be positioned opposite the third side lighting unit (31C). The blank mask (10) may be positioned between the third side lighting unit (31C) and the fourth side lighting unit (31D). The edges of the first side lighting unit (31A), the second side lighting unit (31B), the third side lighting unit (31C), and the fourth side lighting unit (31D) may be adjacent to each other. The first side lighting unit (31A), the second side lighting unit (31B), the third side lighting unit (31C), and the fourth side lighting unit (31D) may surround the blank mask (10). Each of the first side lighting unit (31A), the second side lighting unit (31B), the third side lighting unit (31C), and the fourth side lighting unit (31D) may be turned on or off independently.

[0027] When viewed in a plan view, each of the first side lighting unit (31A), the second side lighting unit (31B), the third side lighting unit (31C), and the fourth side lighting unit (31D) may have a width equal to or greater than the corresponding side of the blank mask (10). Each of the first side lighting unit (31A), the second side lighting unit (31B), the third side lighting unit (31C), and the fourth side lighting unit (31D) may have a horizontal width greater than the maximum horizontal width of the blank mask (10). Each of the first side lighting unit (31A), the second side lighting unit (31B), the third side lighting unit (31C), and the fourth side lighting unit (31D) may have a horizontal width less than or equal to twice the maximum horizontal width of the blank mask (10). The total extension length of the horizontal width of the first side lighting unit (31A), the second side lighting unit (31B), the third side lighting unit (31C), and the fourth side lighting unit (31D) may be 1 to 2 times the perimeter length of the blank mask (10).

[0028] Referring to FIG. 4, the side lighting unit (31) may surround four sides of the blank mask (10). The side lighting unit (31) may be integral. When viewed in a plan view, the side lighting unit (31) may be in the shape of a square ring. The perimeter of the side lighting unit (31) may be greater than the perimeter of the blank mask (10). The perimeter of the side lighting unit (31) may be less than or equal to twice the perimeter of the blank mask (10).

[0029] Referring to FIG. 5, the side lighting unit (31) may include a first side lighting unit (31A), a second side lighting unit (31B), and a third side lighting unit (31C). The second side lighting unit (31B) may be positioned opposite the first side lighting unit (31A). A blank mask (10) may be positioned between the first side lighting unit (31A) and the second side lighting unit (31B). The third side lighting unit (31C) may be positioned adjacent to the first side lighting unit (31A) and the second side lighting unit (31B). The third side lighting unit (31C) may be positioned adjacent to the side of the blank mask (10). The first side lighting unit (31A), the second side lighting unit (31B), and the third side lighting unit (31C) may surround three sides of the blank mask (10).

[0030] Referring to FIG. 6, the side lighting unit (31) may include a first side lighting unit (31A) and a second side lighting unit (31B). The second side lighting unit (31B) may be positioned opposite the first side lighting unit (31A). A blank mask (10) may be positioned between the first side lighting unit (31A) and the second side lighting unit (31B).

[0031] When viewed in a plan view, each of the first side lighting unit (31A) and the second side lighting unit (31B) may have a width equal to or greater than the corresponding side of the blank mask (10). The horizontal width of each of the first side lighting unit (31A) and the second side lighting unit (31B) may be greater than the maximum horizontal width of the blank mask (10). The horizontal width of each of the first side lighting unit (31A) and the second side lighting unit (31B) may be less than or equal to twice the maximum horizontal width of the blank mask (10).

[0032] Referring to FIG. 7, the side lighting unit (31) may include a first side lighting unit (31A). The first side lighting unit (31A) may be positioned adjacent to the side of the blank mask (10). When viewed in a plan view, the first side lighting unit (31A) may have a width equal to or greater than the corresponding side of the blank mask (10). The horizontal width of the first side lighting unit (31A) may be greater than the maximum horizontal width of the blank mask (10). The horizontal width of the first side lighting unit (31A) may be less than or equal to twice the maximum horizontal width of the blank mask (10).

[0033] Referring to FIG. 8, the side lighting unit (31) may surround four sides of the blank mask (10). The side lighting unit (31) may be integral. When viewed in a plan view, the side lighting unit (31) may be ring-shaped. The perimeter of the side lighting unit (31) may be greater than the perimeter of the blank mask (10). The perimeter of the side lighting unit (31) may be one to two times the perimeter of the blank mask (10).

[0034] FIGS. 9 to 11 are cross-sectional views illustrating a blank mask (10) according to embodiments of the technical concept of the present invention. In one embodiment, the blank mask (10) may be a blank mask used in the manufacture of a semiconductor device. For example, the blank mask (10) may have a size of 152 mm X 152 mm X 6.4 mm. The blank mask (10) may include various types of BIM (Binary Mask) blank masks, various types of PSM (Phase Shift Mask) blank masks, or various types of EUV (Extreme Ultraviolet) blank masks.

[0035] Referring to FIG. 9, the blank mask (10) may include various types of blank masks for BIM (Binary Mask). In one embodiment, the blank mask (10) may include a mask substrate (11), a light-blocking layer (14), an anti-reflective coating layer (16), and a resist layer (18).

[0036] The mask substrate (11) may include a material having a low impurity content, excellent chemical durability, and a low coefficient of thermal expansion. For example, the mask substrate (11) may include quartz. The light-blocking layer (14) may be formed on one side of the mask substrate (11). For example, the light-blocking layer (14) may include a metal layer such as a chromium (Cr) thin film. The anti-reflection layer (16) and the resist layer (18) may be stacked sequentially on the light-blocking layer (14).

[0037] Referring to FIG. 10, the blank mask (10) may include a blank mask for various types of Phase Shift Masks (PSM). In one embodiment, the blank mask (10) may include a mask substrate (11), a phase inversion layer (14P), a light-blocking layer (14), an anti-reflective coating layer (16), and a resist layer (18). The phase inversion layer (14P), the light-blocking layer (14), the anti-reflective coating layer (16), and the resist layer (18) may be stacked sequentially on one side of the mask substrate (11). The phase inversion layer (14P) may include MoSi, MoSiN, MoSiO, MoSiON, MoSiCN, MoSiCON, or a combination thereof.

[0038] Referring to FIG. 11, the blank mask (10) may include various types of Extreme Ultraviolet (EUV) blank masks. In one embodiment, the blank mask (10) may include a mask substrate (11), a backside coating layer (12), a reflective layer (13), a capping layer (15), an absorber layer (17), and an anti-reflective layer (19).

[0039] The mask substrate (11) may include a Low Thermal Expansion Material (LTEM). In one embodiment, the back coating layer (12) may be formed on the upper surface of the mask substrate (11). The back coating layer (12) may include a conductive layer for an electrostatic chuck. For example, the back coating layer (12) may include a Cr layer, a CrN layer, or a combination thereof. In one embodiment, the reflective layer (13), the capping layer (15), the absorption layer (17), and the anti-reflection layer (19) may be stacked sequentially on the lower surface of the mask substrate (11). The reflective layer (13) may include a structure in which a plurality of Mo layers and a plurality of Si layers are alternately and repeatedly stacked. The capping layer (15) may include Ru. The absorption layer (17) may include TaN, TaBN, or a combination thereof.

[0040] FIGS. 12 to 14 are schematic diagrams for explaining an inspection system (100) according to embodiments of the technical concept of the present invention.

[0041] Referring to FIG. 12, an inspection system (100) according to embodiments of the technical concept of the present invention may include a stage unit (21), a side illumination unit (31), a camera (56), and an image processing unit (67).

[0042] Referring to FIG. 13, an inspection system (100) according to embodiments of the technical concept of the present invention may include a stage unit (21), a side illumination unit (31), a vertical illumination unit (43), a camera (56), and an image processing unit (67).

[0043] Referring to FIG. 14, an inspection system (100) according to embodiments of the technical concept of the present invention may include a stage unit (21), a side illumination unit (31), an inclined illumination unit (42), a camera (56), and an image processing unit (67).

[0044] FIGS. 15 to 19 are schematic diagrams for explaining inspection methods using an inspection system according to embodiments of the technical concept of the present invention.

[0045] Referring to FIG. 15, the side lighting unit (31) can irradiate an inspection ray (31L) toward the side of the blank mask (10). The inspection ray (31L) may be substantially parallel to the upper surface of the blank mask (10). In one embodiment, the angle formed by the inspection ray (31L) irradiated by the side lighting unit (31) and the upper surface of the blank mask (10) may be 0 degrees to 10 degrees.

[0046] The side lighting unit (31) may be positioned facing the side of the blank mask (10). The thickness of the side lighting unit (31) may be 1 to 2 times the thickness of the blank mask (10). The thickness of the inspection ray (31L) may be 1 to 2 times the thickness of the blank mask (10). The horizontal width of the side lighting unit (31) may be greater than the maximum horizontal width of the blank mask (10). The horizontal width of the side lighting unit (31) may include a configuration similar to that described with reference to FIGS. 3 through 8.

[0047] A first defect (D1) may exist within the mask substrate (11) or adjacent between the mask substrate (11) and the light-blocking layer (14). For example, the first defect (D1) may include a particle, contamination, a crystal defect, or a combination thereof. The mask substrate (11) may serve as a light guide. The inspection ray (31L) may pass through the mask substrate (11) and be irradiated onto the first defect (D1). A first image (BI1) may be generated from the first defect (D1) irradiated by the inspection ray (31L). The first image (BI1) may include a bright image. The first image (BI1) may be detected by the camera (56).

[0048] Referring to FIG. 16, a second defect (D2) may exist inside the mask substrate (11). For example, the second defect (D2) may include a crack. The mask substrate (11) may serve as a light guide. The inspection light (31L) may pass through the mask substrate (11) and be irradiated onto the second defect (D2). A second image (BI2) may be generated from the second defect (D2) irradiated by the inspection light (31L). The second image (BI2) may include a bright image. The second image (BI2) may be detected by the camera (56).

[0049] Referring to FIG. 17, a third defect (D3) may exist at the corner or chamfer of the mask substrate (11). For example, the third defect (D3) may include a chip, a crack, or a combination thereof. The mask substrate (11) may serve as a light guide. The inspection beam (31L) may pass through the mask substrate (11) and be irradiated onto the third defect (D3). Alternatively, the inspection beam (31L) may be irradiated directly onto the third defect (D3). A third image (BI3) may be generated from the third defect (D2) irradiated by the inspection beam (31L). The third image (BI3) may include a bright image. The third image (BI3) may be detected by the camera (56).

[0050] Referring to FIG. 18, a fourth defect (D4) may exist on the mask substrate (11). For example, the fourth defect (D4) may include a particle, contamination, a crystal defect, or a combination thereof. The inspection ray (31L) may be irradiated directly onto the fourth defect (D4). A fourth image (BI4) may be generated from the fourth defect (D4) irradiated by the inspection ray (31L) due to surface diffuse reflection. The fourth image (BI4) may include a bright image. The fourth image (BI4) may be detected by the camera (56).

[0051] Referring to FIG. 19, a fifth defect (D5) adjacent to the surface of the mask substrate (11) may exist. The relative index of refraction of the fifth defect (D5) may be greater than that of the mask substrate (11). For example, the fifth defect (D5) may include a particle, contamination, a crystal defect, or a combination thereof. The mask substrate (11) may serve as a light guide. The inspection ray (31L) may pass through the mask substrate (11) and be irradiated onto the fifth defect (D5). A fifth image (BI5) may be generated from the fifth defect (D5) irradiated by the inspection ray (31L) through refraction. The fifth image (BI5) may include a bright image. The above fifth image (BI5) can be detected by the camera (56).

[0052] The inspection methods described with reference to FIGS. 15 to 19 have been described exemplarily assuming a case where the blank mask (10) includes a configuration similar to one of the various types of BIM (Binary Mask) blank masks shown in FIG. 9, but are not limited thereto, and inspection methods using an inspection system according to embodiments of the technical concept of the present invention may also be applied in cases where the blank mask includes a configuration similar to one of the various types of PSM (Phase Shift Mask) blank masks and various types of EUV (Extreme Ultraviolet) blank masks shown in FIG. 10 and / or FIG. 11.

[0053] The inspection methods described with reference to FIGS. 15 to 19 have been described exemplarily assuming that the inspection system (100) illustrated in FIG. 1 includes the side lighting unit (31), but are not limited thereto, and the inspection methods according to embodiments of the technical concept of the present invention may be applied to independent or various combinations of the inspection system (100) described through FIGS. 1 to 14. For example, the lighting unit (30) may include various combinations selected from a group consisting of the side lighting unit (31), the inclined lighting unit (42), and the vertical lighting unit (43). Inspection rays emitted from each of the side lighting unit (31), the inclined lighting unit (42), and the vertical lighting unit (43) may be controlled independently, selectively, or organically to be irradiated toward the blank mask (10).

[0054] According to inspection methods using an inspection system according to embodiments of the technical concept of the present invention, defects in a wide area such as the surface, interior, corners, and chamfer of the blank mask (10) can be quickly detected. For example, the side lighting unit (31) can generate both an image by diffuse reflection on the surface of the blank mask (10) and an image using the role of a light guide of the mask substrate (11).

[0055] The above-mentioned side lighting unit (31) can be implemented to have various sizes, shapes, and arrangements as described through FIGS. 1 to 14. By varying the sizes, shapes, and arrangements of the above-mentioned side lighting unit (31), an inspection method capable of rapidly detecting defects in a wide area can be provided.

[0056] Although embodiments according to the technical concept of the present invention have been described above with reference to the attached drawings, those skilled in the art will understand that the present invention may be implemented in other specific forms without changing its technical concept or essential features. The embodiments described above should be understood as illustrative in all respects and not restrictive. Explanation of the symbols

[0057] 10: Blank Mask 11: Mask substrate 14: Shading layer 16: Anti-Reflective Coating Layer 18: Resist layer 21: Stage Unit 30: Illumination Unit 31: Side Illumination Unit 42: Inclined lighting unit 43: Vertical lighting unit 56: Camera 67: Image Processing Unit 100: Inspection System SU: Stage Unit IU: Illumination Unit VU: Camera IPU: Image Processing Unit HU: Handling Unit CAS: Clean Air System

Claims

Claim 1 An inspection system comprising: a stage unit on which a blank mask is loaded, wherein a light-blocking layer is laminated on the lower surface of a mask substrate; a side illumination unit positioned opposite to the side of the blank mask and having a plurality of LEDs, which irradiates an inspection beam parallel to the upper surface of the blank mask toward the side of the blank mask; and a camera positioned toward the upper surface of the blank mask, wherein the camera acquires an image of a defect adjacent to the light-blocking layer of the mask substrate. Claim 2 delete Claim 3 delete Claim 4 An inspection system according to claim 1, wherein the thickness of the inspection ray irradiated from the side lighting unit toward the side of the blank mask is 1 to 2 times the thickness of the blank mask. Claim 5 An inspection system according to claim 1, wherein the horizontal width of the side lighting unit is 1 to 2 times the maximum horizontal width of the blank mask. Claim 6 An inspection system according to claim 1, wherein the side lighting unit includes a ring shape, and the perimeter of the side lighting unit is 1 to 2 times the perimeter of the blank mask. Claim 7 An inspection system according to claim 1, further comprising a vertical lighting unit spaced apart from the side lighting unit and positioned adjacent to the camera. Claim 8 In claim 7, an inspection system in which the angle formed between the inspection ray irradiated by the vertical lighting unit and the upper surface of the blank mask is 85 degrees (Degree) to 90 degrees. Claim 9 delete Claim 10 An inspection system comprising: a stage unit for loading a blank mask having a light-blocking layer laminated on the lower surface of a mask substrate; an illumination unit disposed adjacent to the blank mask and having a plurality of LEDs; a camera disposed to face the upper surface of the blank mask; and an image processing unit connected to the camera, wherein the illumination unit comprises: a side illumination unit that irradiates an inspection ray parallel to the upper surface of the blank mask toward the side of the blank mask; an inclined illumination unit that irradiates an inspection ray forming an angle of 15 to 85 degrees with the upper surface of the blank mask toward the upper surface of the blank mask; and a vertical illumination unit that irradiates an inspection ray forming an angle of 85 to 90 degrees with the upper surface of the blank mask toward the upper surface of the blank mask, and wherein the camera acquires an image of a defect adjacent to the light-blocking layer of the mask substrate.

Images