Inspection device and inspection method

Abstract

This inspection device is provided with: a light source unit for irradiating, with light, a wafer having a surface covered with a protection film; a light-receiving unit for receiving reflection light from the wafer or fluorescence emitted as a result of absorption of the light by an additive included in the protection film; a position adjustment means for moving the wafer relative to a measurement unit comprising the light source unit and the light-receiving unit to thereby scan the irradiation position on the wafer; and an analysis unit for analyzing at least an image of the outer circumferential region of the wafer to evaluate the application state of the protection film. The inspection device makes it possible to execute detection of the application state of a protection film on a wafer, which has the protection film layered thereon, with high resolution or in a short period of time.

Description

Inspection device and inspection method

[0001] The present invention relates to a protective film inspection device for inspecting the state of application of a protective film applied to a wafer as a workpiece, and an inspection method using the same.

[0002] In semiconductor manufacturing equipment, when performing laser ablation processes such as laser grooving, laser full cutting, and laser patterning on a wafer, a protective film is sometimes formed by applying a protective film agent containing a water-soluble resin to the processing surface of the workpiece before the ablation process using a method such as spin coating. The protective film prevents processing debris from adhering to the processing surface of the workpiece during the ablation process.

[0003] Furthermore, after processing, debris that melted during processing can be removed along with the protective film by rinsing it away. However, in rare cases, areas where the protective film is not sufficiently formed remain, resulting in coating defects and incomplete coating. In the incomplete coating areas, debris adheres directly to the wafer, leading to manufacturing defects. Therefore, to improve yield, it is necessary to inspect the protective film coating status in advance. Note that the coating status here includes the uniformity of the protective film thickness, and specific examples of abnormalities in the coating status include poor formation of the protective film (incomplete coating). In other words, inspecting the protective film coating status also includes inspecting for poor formation of the protective film.

[0004] Conventionally, when measuring the thickness of a protective film formed on the surface of a substrate having a pattern on the surface, excitation light of a wavelength that causes fluorescence from a material contained as a component of the protective film is irradiated onto the protective film, a condenser lens is placed in the light path, and the fluorescence intensity is measured based on the brightness of the pixels of each image acquired by a light-receiving unit (e.g., an imaging unit). It is known that the thickness of the protective film can then be recognized from correlation data between the previously acquired protective film fluorescence intensity and the protective film thickness, and the calculated protective film fluorescence intensity, as described in Patent Document 1.

[0005] Furthermore, in order to detect the coating state of the protective film with high precision, the device has a reflecting mirror with a reflective surface that reflects fluorescence from the protective film and directs it to a light detection unit, the reflective surface being made up of a part of the curved surface of a spheroid, one of the two foci of the spheroid being located at the part of the protective film that is irradiated with excitation light, and the other being located at the light detection unit, and this is known and described in Patent Document 2.

[0006] JP 2022-178427 A JP 2017-227532 A

[0007] The technique described in Patent Document 1 uses a line scan camera as a light receiving unit having an imaging area longer than the radius of the workpiece, and acquires images by rotating the workpiece, or by using an area sensor camera having an imaging area capable of imaging the entire surface of the workpiece, or an area sensor camera having an imaging area capable of imaging approximately 1 / 4 of the surface of the workpiece, but it is difficult to increase the resolution, and a high-output light source is required to irradiate the excitation light.

[0008] The technique described in Patent Document 2 focuses the fluorescence from the protective film on a reflective surface consisting of part of the curved surface of a spheroid, rotates the wafer, and moves the detection part of the fluorescence detection device in a spiral from the periphery of the wafer W toward the center.Since the measurement is performed while scanning the entire surface of the workpiece, targeting a small area, it was difficult to shorten the detection time.

[0009] The present invention aims to solve at least one of the problems of the above-mentioned conventional technology, and to provide an inspection device or an inspection method that can detect the coating status of a protective film on a wafer coated with the protective film with high resolution or in a short time.

[0010] The present invention has the following configuration for solving the problems.

[0011] The first inspection device of the present invention is an inspection device comprising: a light source unit that irradiates light onto a wafer coated with a protective film on its surface; a light receiving unit that receives reflected light from the wafer or fluorescence emitted when an additive contained in the protective film absorbs the light; a position adjustment means that moves the wafer relative to a measurement unit consisting of the light source unit and the light receiving unit, thereby scanning the irradiation position on the wafer; and an analysis unit that analyzes an image of at least the outer peripheral region of the wafer to evaluate the coating status of the protective film.

[0012] As will be described in detail later, the inventors have found that, in principle, non-uniformities in the protective film on a wafer (specifically, uneven thickness of the protective film, areas left uncoated, etc.) rarely occur only in the central portion of the wafer. In other words, they have found that if no defects occur in the outer peripheral region, the likelihood of defects occurring in the inner peripheral region is significantly low. The analysis unit of the first inspection device reflects this finding and analyzes images of at least the outer peripheral region to evaluate the protective film coating status, thereby enabling detection of wafers with protective film defects in a shorter time than analyzing the entire wafer. Furthermore, the field of view of the imaging unit can be focused on the outer peripheral region, i.e., a more limited area compared to the entire wafer, enabling higher-resolution analysis.

[0013] The second inspection device of the present invention is an inspection device in which, in the first inspection device, the analysis unit analyzes images acquired sequentially as the irradiation position is scanned from the outer peripheral region toward the center, starting with the image of the outer peripheral region.

[0014] In the second inspection device, the analysis unit scans from the outer periphery toward the center and analyzes the images acquired in that order, which enables detection of defects in a shorter time because, as mentioned above, in many cases, defects occur at least in the outer periphery of wafers where defects occur.

[0015] A third inspection apparatus of the present invention is an inspection apparatus that, when an abnormality is detected in the coating state in the second inspection apparatus, stops the scanning and ends the inspection of the wafer.

[0016] In the third inspection system, scanning is stopped and the inspection is terminated when an abnormality is detected, thereby reducing the time required to inspect one wafer. Although abnormalities are typically detected in the acquired image of the outer periphery, the inspection time can also be reduced if the inspection is terminated at that point when an abnormality is detected in the acquired image of the center.

[0017] A fourth inspection apparatus of the present invention is an inspection apparatus in which, in the second inspection apparatus, if an abnormality in the coating state is detected from analysis of the image of the outer peripheral region, scanning toward the center is stopped.

[0018] In the fourth inspection device, scanning is stopped when an abnormality in the coating condition in the outer peripheral region is detected from the image of the outer peripheral region. Since images are acquired sequentially by scanning from the outer peripheral region toward the center, if an abnormality is detected in the outer peripheral region, the inspection is terminated at that point even if image acquisition of the center side has not been completed. As described above, since coating defects rarely occur only in the center side, analysis is started from the image of the outer peripheral region, and when a defect is detected, scanning of the center side and, ultimately, inspection of the wafer is terminated, thereby significantly reducing the inspection time per wafer.

[0019] A fifth inspection apparatus of the present invention is the second inspection apparatus, which switches the inspection mode when no abnormality is detected in the coating state in the outer peripheral region.

[0020] Based on the above findings, if no abnormality is detected in the coating condition in the outer peripheral region, the possibility of detecting an abnormality in the inner peripheral region is significantly low. The inspection device of the fifth embodiment is configured to switch the inspection mode depending on the inspection results of the outer peripheral region, so the inspection time can be adjusted by, for example, changing the scanning method (speed, etc.) or the imaging method (photographing interval). Specifically, by switching the inspection of the inner peripheral region to a mode (setting) that increases the scanning speed (feed rate) and / or increases the imaging interval, the inspection time per wafer can be further reduced.

[0021] A sixth inspection apparatus of the present invention is an inspection apparatus according to any one of the first to fifth inspection apparatuses, wherein the outer peripheral region is predetermined as a range from the outer edge of the wafer to within 50% of the radius of the wafer.

[0022] In the sixth inspection apparatus, the outer peripheral region is determined within a predetermined range according to the radius of the wafer, so that both a reduction in inspection time per wafer and high resolution are achieved.

[0023] A seventh inspection apparatus of the present invention is any one of the first to fifth inspection apparatuses, wherein the outer peripheral area is determined according to the size of the field of view of the light receiving unit.

[0024] By determining the size of the outer peripheral region according to the size of the field of view of the light receiving unit, it is possible to adjust the number of scans required to complete image acquisition of the outer peripheral region. For example, the size of the outer peripheral region can be set to twice or three times the size of the field of view. Typically, a size of about 0.8 to 5 times is preferable. This adjustment makes it possible to achieve both a shorter inspection time per wafer and high resolution.

[0025] The eighth inspection apparatus of the present invention is the seventh inspection apparatus, wherein the outer peripheral region is an area having a width equal to the size of the field of view of the light receiving unit, based on the outer edge of the wafer.

[0026] By making the outer peripheral region an area with a width equal to the size of the field of view of the imaging unit, image acquisition of the outer peripheral region can be completed with a single scan of the periphery, thereby further shortening the inspection time per wafer.

[0027] A first inspection method of the present invention is a method for inspecting the application status of a protective film on a wafer having a protective film coated on its surface, and includes irradiating the wafer with light and receiving reflected light, or irradiating the wafer with light and receiving fluorescence emitted when an additive contained in the protective film absorbs the light, scanning the light irradiation position on the wafer, and analyzing an image of at least the outer circumferential region of the wafer to evaluate the application status of the protective film.

[0028] The first inspection method reflects the above findings and analyzes an image of at least the outer periphery region to evaluate the coating condition of the protective film, thereby enabling detection of wafers with defective protective films in a shorter time than analyzing the entire wafer. Furthermore, the imaging range at one time can be focused on the outer periphery region, i.e., a more limited area compared to the entire wafer, enabling analysis with higher resolution.

[0029] A second inspection method of the present invention is an inspection method in which, in the first inspection method, the images are acquired by scanning from the outer peripheral region toward the center, and the analysis is performed in order starting from the images of the outer peripheral region.

[0030] In the second inspection method, the analysis unit analyzes images in order starting from the outer peripheral region, thereby realizing detection of defects in a shorter time.

[0031] A third inspection method of the present invention is the second inspection method, wherein, when an abnormality is detected in the coating state, the scanning is stopped and the inspection of the wafer is terminated.

[0032] In the third inspection method, scanning is stopped and the inspection is terminated when an abnormality is detected, thereby reducing the time required to inspect one wafer. Although an abnormality is typically detected in an acquired image of the outer periphery, if an abnormality is detected in an acquired image of the inner periphery, the inspection time can also be reduced by terminating the inspection at that point.

[0033] According to the present invention, an inspection device and an inspection method are provided that can detect the coating condition of a protective film on a wafer with a protective film stacked thereon with high resolution or in a short time.

[0034] FIG. 1 is a block diagram of a laser processing apparatus including an inspection apparatus according to an embodiment of the present invention. FIG. 2 is a configuration diagram of an inspection apparatus according to an embodiment of the present invention. FIG. 3 is a plan view showing a typical example of unevenness of a protective film on a wafer. FIG. 4 is a plan view showing a typical example of unevenness of a protective film on a wafer. FIG. 5 is a plan view showing a typical example of unevenness of a protective film on a wafer. FIG. 6 is a diagram showing a conventional inspection method. FIG. 7 is a diagram showing an inspection method according to an embodiment. FIG. 8 is an explanatory diagram showing an example of determining an outer circumferential region. FIG. 9 is an explanatory diagram showing an example of determining an outer circumferential region. FIG. 10 is an explanatory diagram of a rough inspection mode in which the center side is inspected after inspecting the outer circumferential region. FIG. 11 is an explanatory diagram of a rough inspection mode in which the center side is inspected after inspecting the outer circumferential region. FIG. 12 is a flowchart showing processes from coating a protective film to inspection according to an embodiment.

[0035] 1A is a block diagram of a laser processing apparatus including an inspection apparatus according to the present invention. As shown in FIG. 1A, the laser processing apparatus 10 includes a control unit 12, a laser processing unit 100, a protective film coating / cleaning unit 200, and a transport unit 300.

[0036] The laser processing unit 100 is a device for performing laser processing (laser ablation processing) on ​​a wafer W held by suction on a table T1.

[0037] The protective film coating / cleaning unit 200 is an apparatus for coating the protective film PL onto the wafer W held by suction on the table T2 and cleaning the wafer W. In this embodiment, the protective film coating / cleaning unit 200 further evaluates the coating condition of the protective film PL applied to the wafer W (for example, the coating condition of the thickness, whether or not any part is left uncoated).

[0038] The transport unit 300 is a device that transports the wafer W between the table T1 of the laser processing unit 100 and the table T2 of the protective film coating / cleaning unit 200. The transport unit 300 includes, for example, an arm for suction-holding the wafer W, and a movement mechanism (e.g., a ball screw mechanism, a motor, etc.) for moving the arm in the transport direction (X and Y directions). The transport unit 300 may include a cassette for storing the wafer W in a state where a dicing tape is attached to the surface opposite to the surface on which devices are formed and the wafer W is attached to a frame (not shown).

[0039] The control unit 12 is a device that controls each part of the laser processing apparatus 10. The control unit 12 includes a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), a storage device (e.g., a hard disk, etc.), an operation member for receiving operation input from a user, and a display that displays a graphical user interface (GUI) for operating the laser processing apparatus 10. In the control unit 12, various programs such as a control program stored in the ROM are loaded into the RAM, and the programs loaded into the RAM are executed by the CPU, thereby controlling the functions of each part of the laser processing apparatus 10. The control unit 12 can be realized by a general-purpose computer such as a personal computer or a microcomputer. The control unit 12 also includes an analysis unit 121 that performs image analysis, etc., as described below.

[0040] In this embodiment, the laser processing unit 100, the protective film coating / cleaning unit 200, and the transport unit 300 are controlled by a common control unit 12, but a separate control unit may be provided for each unit.

[0041] As shown in FIG. 1A, the laser processing unit 100 includes a laser processing section 102, an imaging section 104, and a table driving section 106.

[0042] The laser processing unit 102 includes a laser oscillator that pulses laser light and a laser optical system that focuses the laser light output from the laser oscillator onto the surface of the wafer W. The laser oscillator may be, for example, a semiconductor laser pumped Nd:YAG (Yttrium Aluminum Garnet) laser or Nd:YVO ４ A laser or the like can be used. The laser oscillator is capable of outputting laser light of a wavelength that is absorbed by the wafer W (e.g., a silicon wafer). The laser optical system is capable of adjusting the spot diameter of the laser light at the processing point on the surface of the wafer W.

[0043] The imaging unit 104 is a device that captures an image of the surface of the wafer W, and includes, for example, a CCD (Charge Coupled Device) camera or an IR (Infrared) camera. The imaging unit 104 is provided, for example, near the processing head of the laser processing unit 102, and captures an image of the surface of the wafer W. Note that the imaging unit 104 may also be configured to serve as part of the optical system of the laser processing unit 102.

[0044] The table driving unit 106 is a device that moves the table T1 in the processing feed direction (X and Y directions) and the rotation direction (θ direction). The table driving unit 106 includes a ball screw mechanism and a motor for moving the table T1 in the X and Y directions, and a mechanism (motor, etc.) for rotating the table T1 in the θ direction.

[0045] The control unit 12 detects the position of the planned dividing line CL by performing image processing such as pattern matching on the image of the surface of the wafer W captured by the imaging unit 104. Then, the control unit 12 performs alignment to adjust the position of the laser light by adjusting the position of the wafer W relative to the processing head of the laser processing unit 102 according to the detected position of the planned dividing line CL.

[0046] In this embodiment, the table T1 is movable in the X, Y, and θ directions, but the machining head 102A may be movable in the X, Y, and θ directions, or both may be movable.

[0047] As shown in FIG. 1A, the protective film coating / cleaning unit 200 includes a protective film detection unit 202 , a protective film coating mechanism 204 , a table T2 , a cleaning mechanism 206 , and a table driving unit 208 .

[0048] The protective film detection unit 202 evaluates the coating condition of the protective film PL formed on the surface of the wafer W. As will be described in detail later, the protective film detection unit 202 includes a light source unit 2 and a light receiving unit 1 as hardware.

[0049] The protective film applying mechanism 204 has a discharge port for dropping the material (protective film agent) of the protective film PL onto the surface of the wafer W. If the material of the protective film PL is liquid at room temperature (15°C to 25°C), the protective film applying mechanism 204 does not need to include a heating mechanism for the protective film agent. In this case, the protective film applying mechanism 204 may include a drying mechanism (heater, etc.) for removing the solvent, etc. after the film is formed.

[0050] The configuration of the protective film application mechanism 204 may vary depending on the type of protective film agent (specifically, the type of resin contained therein, etc.) For example, when a resin that is solid at room temperature (15°C to 25°C) is used as the material, the protective film application mechanism 204 may include a heating mechanism (heater, etc.) for melting the resin, and a tank for temporarily storing the protective film agent containing the molten resin (neither of which is shown).

[0051] The protective film agent is liquid when applied and may contain a resin as a main component and, if necessary, other components. Examples of the resin include, but are not limited to, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol having five or more ethyleneoxy repeating units, polyethylene oxide, methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, polyacrylic acid, polyvinyl alcohol-polyacrylic acid block copolymer, polyvinyl alcohol-polyacrylic acid ester block copolymer, and polyglycerin. These resins may be used alone or in combination of two or more.

[0052] Other components include solvents, light absorbers, etc. The solvent is not particularly limited, as long as it can dissolve and / or disperse the resin, which is the main component. Furthermore, from the viewpoint of easier cleaning, the solvent is preferably water or a water-soluble organic solvent. The light absorber is preferably one that can absorb the wavelength of the laser beam used in laser processing, for example, one that absorbs light with a wavelength of 250 nm or more and 450 nm or less. Examples of such light absorbers include benzophenone-based, benzotriazole-based, triazine-based, and benzoate-based ultraviolet absorbers. Furthermore, some light absorbers absorb light of a specific wavelength and emit fluorescence. For example, by using caffeic acid, chlorogenic acid, or the like in addition to benzophenone-based absorbers, strong fluorescence can be obtained upon ultraviolet irradiation.

[0053] The table driving unit 208 includes a mechanism (motor, etc.) for moving and rotating the table T2 on which the wafer W is held by suction.

[0054] The cleaning mechanism 206 is a device for cleaning the wafer W, and includes, for example, a nozzle for spraying a cleaning liquid (e.g., water or a liquid soluble in the protective film PL) onto the surface of the wafer W, and a mechanism for supplying the cleaning liquid (e.g., a tank or a pipe, etc.). The cleaning mechanism 206 may also include a mechanism for spraying air (e.g., compressed air).

[0055] In the laser processing apparatus 10, the protective film detection unit 202 is included in the protective film application / cleaning unit 200. However, the protective film detection unit 202 may be incorporated into the laser processing apparatus 10 as an independent unit, or may be included in the laser processing unit 10. When the protective film detection unit 202 is included in the laser processing unit 10, the table T1 and the table drive unit 106 may be used instead of the table T2 and the table drive unit 208.

[0056] Next, the processing procedure for the wafer W using the laser processing apparatus 10 will be described. First, a protective film PL is applied by spin coating. While the table T2 is rotated in the θ direction by the table drive unit 208, a protective film agent is dropped from a discharge port near the center of the wafer W. Then, centrifugal force moves the liquid resin toward the outer periphery of the surface of the wafer W, and the protective film agent spreads to a substantially uniform thickness over the surface of the wafer W, forming a protective film agent layer. Then, when the solvent is removed from the protective film agent layer (typically by drying), the protective film PL is formed. Next, the protective film detection unit 202 evaluates the application status of the protective film PL. Note that the protective film PL may also be applied by spray coating.

[0057] Next, the transfer unit 300 picks up and transfers the wafer W from the table T2 of the protective film coating / cleaning unit 200, and places it on the table T1 of the laser processing unit 100. After the wafer W is placed on the table T1 with the surface on which the devices are formed facing up, the back side of the wafer W is sucked by a suction source (vacuum generator, such as an ejector or pump) (not shown), thereby suction-holding the wafer W on the surface of the table T1.

[0058] Next, the attitude of the table T1 is adjusted so that the planned dividing lines of the wafer W (for example, arranged in a grid pattern in the X and Y directions) are parallel to the X direction. Then, a laser beam is focused on the planned dividing lines on the surface of the wafer W, and the table T1 is moved in the X direction. By repeating this process, laser ablation processing is performed along the planned dividing lines along the X direction. As a result, laser grooves are formed on the surface of the wafer W along the planned dividing lines. Here, the depth of the laser grooves need only be deep enough to cut the device layers formed on the wafer W.

[0059] Next, the table T1 is rotated 90° in the θ direction by the table driving unit 106, and the laser ablation process is repeated. This forms laser grooves along all of the planned division lines. As a result, a grid-like pattern of laser grooves is formed on the wafer W along the planned division lines. In a subsequent dicing process, the wafer W is divided into individual device chips, starting from these laser grooves.

[0060] Next, the wafer W is cleaned. In the cleaning process, a cleaning liquid is sprayed from the nozzle of the cleaning mechanism 206 to wash away debris generated by the laser ablation process, the protective film PL, and the like. In the cleaning process, a cleaning liquid that is soluble in the material of the protective film PL may be sprayed to remove the protective film PL. When the protective film PL is PVC, for example, cyclohexanone, tetrahydrofuran, nitrobenzene, ethyl methyl ketone, dioxane, or the like may be used as the cleaning liquid. In the cleaning process, similar to the protective film PL coating process, the table T2 may be rotated to ensure that the cleaning liquid spreads evenly over the surface of the wafer W.

[0061] Next, an inspection apparatus according to an embodiment of the present invention will be described. FIG. 1B is a configuration diagram of an inspection apparatus 400. The inspection apparatus 400 includes a protective film detection unit 202 including a light-receiving unit 1 and a light source unit 2, a table T2, a table drive unit 208, and an analysis unit 121. The light-receiving unit 1 and the light source unit 2 (collectively referred to as a measurement unit) are included in the protective film detection unit 202. The protective film detection unit 202, the table T2, and the table drive unit 208 are included in the protective film coating / cleaning unit 200, and the analysis unit 121 is a part of the function of the control unit 12. In other words, the inspection apparatus 400 is included in the laser processing apparatus 10.

[0062] When inspecting the protective film PL, the wafer W is placed on the table T2. The table T2 is equipped with a rotation mechanism 3 and a horizontal movement mechanism 4. With the above configuration, the irradiation position of light from the light source unit 2 (the position where the image is acquired by the light receiving unit 1) is scanned and moved across the wafer W. That is, the measurement unit and the wafer W are moved relative to each other by the table T2, and the irradiation position is scanned across the wafer W. The table T2 functions as a position adjustment device. Note that, depending on the method of scanning and moving the irradiation position, the position adjustment device may have a configuration other than that described above. For example, if the irradiation position is moved around the periphery of the wafer W, the position adjustment mechanism (in this case, the table T2) does not need to be equipped with the horizontal movement mechanism 4. On the other hand, it is preferable that the position adjustment mechanism has the function of rotating and horizontally moving the irradiation position across the wafer W, since this enables measurement of the central portion of the wafer W in addition to the periphery. In the above embodiment, an example has been described in which the table T2 functions as the position adjustment means, but the measurement unit may be configured to be movable instead of (or in addition to) the table T2. In this case, the position adjustment means can move the position of the measurement unit.

[0063] The present inventors have carefully analyzed the conditions and causes of non-uniformity of the protective film (typically, uneven coating or uncoated areas) that occurs when a protective film agent containing a resin (e.g., a water-soluble resin) is applied to a wafer to cover the wafer W with the protective film. Figure 2 is a plan view showing a typical example of non-uniformity of the protective film obtained as a result of analyzing coating defects and uncoated areas using spin coating or a film-forming method involving rotation of the wafer W. The inventors' investigations have found that the majority of coating defects and uncoated areas can be classified into those shown in Figures 2A, 2B, and 2C.

[0064] 2A shows a situation where a shortage of protective film agent (lack of protective film agent) has resulted in uncoated areas on the outer edge. In this case, the uncoated areas (defects) are scattered only in the outer peripheral region of the wafer W. Specifically, in the case of a wafer W with a diameter of 300 mm, uncoated areas are likely to occur in the region up to about 5 cm from the outer edge.

[0065] 2B shows a situation where a foreign particle is present in the inner peripheral region of the wafer W, causing an uncoated area. In this case, the uncoated area radiates from the foreign particle toward the outer peripheral edge. Therefore, regardless of the location of the foreign particle, the uncoated area occurs from the foreign particle toward the outer peripheral region.

[0066] 2C shows a situation where droplets (e.g., water droplets) are present on the surface of the wafer W. In many cases, these droplets are the solvent of the protective film agent (e.g., water if the protective film agent is water-soluble), and these water droplets cause disturbances in the protective film agent layer, specifically, the formed protective film is re-dissolved, resulting in uncoated areas that trail toward the outer edge.

[0067] When forming a protective film on a wafer W, generally, the wafer W is rotated in most cases, and in this case, as is clear from the typical example described above, the inventors' investigations have revealed that uncoated areas occur at least in the outer peripheral region of the wafer W. In other words, it has become clear that if there are no defects in the outer peripheral region, it is extremely rare for defects to exist on the central side (inner peripheral region).

[0068] Fig. 3A is a diagram showing a conventional inspection method. Fig. 3B is a diagram showing an inspection method according to an embodiment. In Fig. 3A, when the diameter of the wafer W is 300 mm, the size of the field of view of the light receiving unit 1 is 150 mm x 150 mm, the surface of the wafer W is divided into four sections, and the irradiation position is moved to acquire images. The irradiation position is moved by moving the light receiving unit 1 and / or the wafer W.

[0069] 3B, the field of view is set to 15 mm x 15 mm, and the field of view is positioned in the outer peripheral region, and the irradiation position is scanned in the circumferential direction to acquire an image. The irradiation position is moved by rotating the light-receiving unit 1 or the wafer W as shown by the arrow.

[0070] As described above, defects such as uncoated areas are likely to occur in the outer peripheral region of the wafer W and are rarely found in the center. Comparing Figures 3A and 3B, the embodiment of Figure 3B is configured to narrow the field of view and primarily measure the outer peripheral region, and to measure the inner peripheral region as needed, thereby improving the pixel resolution of the captured image with the same light-receiving unit 1. Furthermore, for the same resolution, the embodiment of Figure 3B can use a less expensive light-receiving unit 1. Note that narrowing the field of view and improving pixel resolution can be achieved by increasing the magnification of the lens system, even if the number of pixels of the image sensor of the light-receiving unit 1 is the same.

[0071] Specifically, the embodiment of FIG. 3B has a field of view that is 1 / 10 the size of that of FIG. 3A, which is 0.1 mm / pixel in FIG. 3A but 0.01 mm / pixel in FIG. 3B, thereby increasing the pixel resolution by 10 times.

[0072] Furthermore, since the irradiation area is reduced to 1 / 100, if the illuminance is kept constant, the total energy required for illumination is also reduced to 1 / 100, which reduces the amount of light and reduces lighting costs. Note that it is also possible to increase the size of the field of view to acquire an image and inspect only the outer periphery area, but a high-resolution light-receiving unit 1 would be expensive.

[0073] When only the outer peripheral region is to be inspected, the light receiving unit 1 or the wafer W only needs to rotate once, thereby shortening the measurement time. For example, in Fig. 3A, if the field of view is set to the same as in Fig. 3B and the detection unit is moved spirally from the periphery of the wafer W toward the center to scan the entire surface of a wafer W with a diameter of 300 mm, the total number of rotations will be 500, and the total imaging time will be 10 seconds. In contrast, according to the method shown in Fig. 3B, only one rotation is required, so the total imaging time will be 0.02 seconds, and the measurement time can be reduced to 1 / 500.

[0074] Furthermore, if an unpainted area is detected during image acquisition, the image acquisition process is stopped and the wafer W is treated as abnormal, further shortening the measurement time from image capture to inspection. Specifically, the image of the outer peripheral region acquired first is analyzed first, and if an abnormality (e.g., an unpainted area) is detected, subsequent scanning and inspection are halted. Image acquisition and analysis do not need to be synchronized (i.e., image acquisition of the inner peripheral region may begin while image analysis of the outer peripheral region is in progress). Even if image acquisition is performed first, subsequent image acquisition of the central region (inner peripheral region) may be halted upon detection of an abnormality in the outer peripheral region. This configuration significantly reduces the inspection time per wafer W.

[0075] In order to shorten the imaging time, it is advantageous to increase the field of view of the light-receiving unit 1, so it is preferable to determine the field of view in accordance with the actual size of the unpainted area, the pixel resolution (or the number of pixels of the imaging element) of the light-receiving unit 1. For example, if the pixel resolution is sufficient based on the actual size of the unpainted area, the field of view can be increased to shorten the measurement time, and if the actual size of the unpainted area is small, the field of view can be reduced for measurement.

[0076] 4A to 4C are explanatory diagrams showing examples of determining the peripheral region. As described above, the narrower the peripheral region to be inspected, the shorter the inspection time and the higher the inspection resolution. On the other hand, by making the peripheral region wider, the results are more likely to reflect the protective film coating status of the entire wafer W (improving inspection accuracy). In light of the above, it is preferable to determine the peripheral region as follows: (1) As shown in FIG. 4A, the peripheral region is set to a range from the outer edge of the wafer W to within 50% of the radius of the wafer W. (2) As shown in FIG. 4B, in the case of a wafer W with a diameter of 300 mm, the peripheral region is set to 30 to 60 mm, more preferably 30 to 50 mm, or 20 to 40% of the radius of the wafer W from the outer edge.

[0077] (3) As shown in Figure 4C, when the diameter of the wafer W is 300 mm, the size of the field of view of the light receiving unit 1 is 10 to 20 mm x 10 to 20 mm, more preferably 15 mm x 15 mm, and the outer peripheral region is 10 to 20 mm, more preferably 15 mm, from the outer edge of the wafer W.

[0078] (4) The peripheral region may be a range from the outer edge to approximately 1 to 10 times the chip size, which is the size of the semiconductor chip. In this case, a certain width from the edge of the wafer W is excluded from the consideration. This is because there is often no problem even if a protective film is not formed in this range. For example, in the case of a wafer W diameter of 300 mm, the standard chip size is several millimeters to several tens of millimeters, so for a 10 mm square chip, the peripheral region is a range of approximately 10 mm from the inside of the wafer peripheral cut region.

[0079] (5) The outer peripheral region is defined as the region from the outer edge of the wafer W to the field of view of the light-receiving unit 1. For example, the size of the field of view is set to 15 mm x 15 mm based on the pixel resolution, shutter speed, etc. of the light-receiving unit 1, and the outer peripheral region is defined as the region from the outer edge of the wafer W to 15 mm.

[0080] In (1) to (5), the determined peripheral region may be an imaging region from which an image is acquired, or an inspection region from which unpainted areas are inspected in the acquired image. In other words, "acquiring an image of the peripheral region" may include acquiring only an image of the peripheral region and acquiring an image of an area including the peripheral region. Furthermore, "analyzing an image of the peripheral region" may include analyzing an image including only the peripheral region as is, and analyzing an image of the peripheral region portion from an image including the peripheral region. As one embodiment, from the viewpoint of shortening the inspection time per wafer W, acquiring an image of almost only the peripheral region and analyzing that image is preferable. In this case, excellent effects can be obtained without using an expensive light-receiving unit 1.

[0081] On the other hand, as a form of acquiring an image including the outer peripheral region and then analyzing a portion of that image (the outer peripheral region), for example, in the case of a wafer W diameter of 300 mm, if the pixel resolution of the light-receiving unit 1 is sufficiently high, the field of view can be enlarged to 150 mm x 150 mm to acquire the captured image. In this case, too, the outer peripheral region may be determined as in (1) to (5). In this form, the time required to acquire an image of the entire wafer is shortened.

[0082] 5A and 5B are explanatory diagrams of a rough inspection mode in which the outer peripheral region is inspected and then the center region is inspected. If there is no unpainted area in the outer peripheral region, it is unlikely that there is an unpainted area in the inner peripheral region. However, just to be sure, the inner peripheral region can also be inspected. In this case, the outer peripheral region and the inner peripheral region may be inspected using the same inspection method. However, to shorten the inspection time per wafer W, it is also preferable to inspect the outer peripheral region and the inner peripheral region by switching the inspection mode. Specifically, as shown in FIGS. 5A and 5B, when inspecting the inner peripheral region, it is preferable to use a "rough inspection mode" in which at least one of the following parameters is changed from the inspection of the outer peripheral region: scanning speed (feed rate), scanning direction (feed direction), number of images acquired, image acquisition interval, and field of view. FIG. 5A shows a method of inspecting the inner peripheral region by changing the feed rate, and FIG. 5B shows a method of changing the feed method.

[0083] 5A shows that the wafer W is scanned and inspected around the circumference in the outer peripheral region, and then the inner peripheral region is sequentially inspected in the same manner. At this time, the inner peripheral region is inspected at a faster feed rate than the outer peripheral region (the dashed line indicates a faster feed rate). Generally, the radius of rotation is smaller in the inner peripheral region than in the outer peripheral region, so the relative speed between the wafer W and the light-receiving unit 1 is slower. Therefore, even if the feed rate is increased in the inner peripheral region, the resolution is not reduced. In particular, if the feed rate is increased in proportion to the change in the radius of rotation, the resolution is less likely to be reduced.

[0084] Furthermore, since the rough inspection mode inspects the inner peripheral region where unpainted areas are rare, the resolution may be reduced, for example, by making the field of view larger (wider) than the outer peripheral region to shorten the inspection time. Furthermore, the inner region may be inspected thoroughly, or may be inspected in a "discrete" manner. "Discrete" inspection means that images are acquired by thinning out or by setting up regions (times) where no images are taken, or that images are acquired continuously without thinning out and the inspection region is thinned out or by setting up regions where no inspection is taken.

[0085] Furthermore, it is preferable to thin out the captured images, or to thin out the number and areas of the inspection areas by weighting them according to the position on the wafer W. For example, it is preferable to thin out the number and areas to be small when the radial position to be imaged is large, and to thin out the number and areas to be large in proportion to the radial position as it decreases.

[0086] The arrows in Figure 5B indicate that the outer peripheral region is inspected, and then the X-axis and Y-axis are scanned to sequentially inspect the inner peripheral region. After the outer peripheral region is inspected by rotating the wafer W (or the light receiving unit 1), no further rotation is required, making operation and processing relatively easy. For example, if the wafer W is moved in a zigzag pattern as shown by the arrows, it is only necessary to move one axis along the X-axis and the other along the Y-axis, making control easy. This movement method also makes it easy to achieve uniformity even when inspecting discontinuously. Furthermore, if the wafer W is fed in the same way as it is fed during processing, control by the control unit 12 (e.g., software setting) is likely to be easier.

[0087] Here, the procedure from application of the protective film by the protective film coating / cleaning unit 200 to inspection will be described in detail. FIG. 6 is a flowchart showing the procedure from application of the protective film by the protective film coating / cleaning unit 200 to inspection. As described above, the inspection device 400 can also be said to be part of the protective film coating / cleaning unit 200. In the flow of FIG. 6, the flow enclosed by a dashed frame marked with reference numeral S200 (i.e., the entire flow) is performed by the protective film coating / cleaning unit 200. Of these, the flow enclosed by a dashed frame marked with reference numeral S100 is performed by the inspection device 400.

[0088] First, in step S1, the protective film coating / cleaning unit 200 applies a protective film agent containing a resin to form a protective film agent layer on the wafer W, and then dries and removes the solvent to form a protective film on the wafer W. The method for forming the protective film is as described above, and may be, for example, spin coating.

[0089] Next, the light source unit 2 irradiates the irradiation position in the outer peripheral region of the wafer W with light, and the light receiving unit 1 acquires an image of the irradiation position (step S2). At this time, the light received by the light receiving unit 1 may be reflected light from the wafer W or fluorescence emitted when an additive contained in the protective film absorbs light. Acquisition of this image may be performed by a measurement unit controlled by the control unit 12.

[0090] When the image is acquired, analysis of the acquired image is started in parallel by the analysis unit 121 (step S10). Image acquisition and analysis of the acquired image may be performed synchronously, but if they are performed sequentially, neither one becomes the rate limiting factor, and the examination can be performed more efficiently.

[0091] Meanwhile, the position adjusting means sequentially scans the irradiation position from the outer periphery of the wafer W toward the center (step S3), and an image is acquired (step S4). The acquired image is saved in, for example, a BMP file format.

[0092] The image acquired in step S4 is sent (input) to the analysis unit 121 (step S11). Next, the analysis unit 121 analyzes the acquired image to evaluate the application status of the protective film. While the method for evaluating the application status of the protective film is not particularly limited, when the absorbance (absorbance of ultraviolet light) of the protective film is used, the application status of the film thickness can be evaluated from the difference in contrast within the acquired image. Specifically, areas with a large film thickness have a large absorbance and are displayed darker, while areas with a small film thickness or areas that have not been coated have a small absorbance and are displayed brighter. The application status can be evaluated by comparing these with a predetermined standard or a reference image. Furthermore, when the fluorescence of the protective film (fluorescence of the additive) is used, areas with a large film thickness have a large fluorescence and are displayed brighter, while areas with a small film thickness or areas that have not been coated have a small fluorescence and are displayed darker. The application status can be evaluated by comparing these with a predetermined standard or a reference image (step S12). The coating condition is typically preferably evaluated by evaluating the unevenness of the protective film, that is, whether or not there are any uncoated areas.

[0093] The processing from step S2 to step S5 and the processing from step S10 to step S12 may be synchronized, but it is preferable not to synchronize them, in other words, to perform the unpainted area determination while acquiring the image. In other words, it is preferable to perform the image capture and image processing in parallel. This eliminates the need to stop the operation of acquiring the captured image regardless of the time required for image processing, and therefore the entire processing can be completed in a short time.

[0094] If it is determined in step S12 that there is an uncoated area or an incompletely coated area, an error (failure) is output (step S14). Steps S11 and S12 are repeated until the specified number of captured images have been processed, and if it is determined in step S12 that there is no incompletely coated area, the inspection process ends (step S13).

[0095] If an output from step S14 is received and an error is found, the measurement is forcibly terminated (step S20). After the forcible termination, the wafer W is cleaned (step S21). After cleaning, the protective film is applied again, and imaging and inspection are started. As a result, as soon as an incomplete coating is found, cleaning and recoating are performed, and by inspecting from the outer periphery where there is a high possibility of incomplete coating toward the center, defects can be quickly found and the protective film can be recoated if an incomplete coating is found.

[0096] The output from step S14 is received, and if there are no errors after processing the specified number of captured images, the inspection and protective film process is terminated (step S7).

[0097] As described above, the inspection method of this embodiment evaluates the coating condition of the protective film laminated on the wafer based on an image acquired of the outer periphery region, and therefore can detect wafers with defective protective films in a shorter time than analyzing the entire wafer W. Furthermore, the field of view of the light receiving unit can be focused on the outer periphery region, i.e., a more limited region compared to the entire wafer, enabling higher-resolution analysis.

[0098] REFERENCE SIGNS LIST 1...light receiving unit 2...light source unit 3...rotation mechanism 4...horizontal movement mechanism 10...laser processing device 12...control unit 100...laser processing unit 102...laser processing section 121...analysis section 104...imaging section 106...table driving section 200...protective film application / cleaning unit 202...protective film detection section 204...protective film application mechanism 206...cleaning mechanism 208...table driving section 300...transport unit 400...inspection device W...wafer PL...protective film

Claims

1. An inspection device comprising: a light source unit that irradiates light onto a wafer coated with a protective film on its surface; a light receiving unit that receives reflected light from the wafer or fluorescence emitted when an additive contained in the protective film absorbs the light; a position adjustment means that moves the wafer relative to a measurement unit consisting of the light source unit and the light receiving unit, and scans the irradiation position on the wafer; and an analysis section that analyzes an image of at least the outer periphery of the wafer to evaluate the coating condition of the protective film.

2. The inspection device according to claim 1, wherein the analysis unit analyzes images sequentially acquired as the irradiation position is scanned from the outer peripheral region toward the center, starting with the image of the outer peripheral region.

3. The inspection device according to claim 2, wherein if an abnormality is detected in the coating state, the scanning is stopped and the inspection of the wafer is terminated.

4. The inspection device according to claim 2, wherein scanning toward the center is stopped if an abnormality in the coating state is detected from analysis of the image of the outer peripheral region.

5. The inspection device according to claim 2, wherein the inspection mode is switched when no abnormality is detected in the coating state in the outer peripheral region.

6. An inspection device according to any one of claims 1 to 5, wherein the outer peripheral region is predetermined as a range within 50% of the radius of the wafer from the outer edge of the wafer.

7. An inspection device according to any one of claims 1 to 5, wherein the outer peripheral area is determined according to the size of the field of view of the light receiving unit.

8. An inspection device according to claim 7, wherein the outer peripheral area is an area having a width equal to the size of the field of view of the light receiving unit, based on the outer edge of the wafer.

9. A method for inspecting the coating condition of a protective film on a wafer having a surface coated with the protective film, comprising: irradiating the wafer with light and receiving reflected light, or irradiating the wafer with light and receiving fluorescence emitted when an additive contained in the protective film absorbs the light; scanning the light irradiation position on the wafer; and analyzing an image of at least the outer circumferential region of the wafer to evaluate the coating condition of the protective film.

10. The inspection method according to claim 9, wherein the images are acquired by scanning from the outer peripheral region toward the center, and the analysis is performed in order starting from the images of the outer peripheral region.

11. The inspection method according to claim 10, wherein, if an abnormality is detected in the coating state, the scanning is stopped and the inspection of the wafer is terminated.

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