Protective film inspection method and protective film inspection device

Abstract

To provide a protective film inspection method and a protective film inspection device that allow protective film inspection with high accuracy based on film thickness measurement considering fluorescence color fading.SOLUTION: The protective film inspection method is a method for inspecting the application state of a protective film applied to a wafer and including a light absorber. The protective film inspection method has: a measurement step S2 of measuring the fluorescence intensity of fluorescence emitted by the light absorber that is irradiated with excitation light and emits light; an inspection step S3 of inspecting the application state of the protective film on the basis of fluorescence intensity data obtained in the measurement step S2; and a color fading step S1 of irradiating the protective film with the excitation light to cause the color of the light absorber to be faded before the measurement step S2.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a protective film inspection method and a protective film inspection device. [Background technology]

[0002] Laser ablation processing is used in semiconductor manufacturing, which can cause melted debris to adhere to the device layer. Therefore, a protective film made of a water-soluble resin is typically formed on the wafer surface before laser ablation processing. This protective film protects the device layer from debris generated during laser ablation processing. After laser ablation processing, the debris can be washed away along with the protective film.

[0003] The protective film is applied by methods such as spin coating, but coating defects occasionally occur. Specifically, there are cases where areas of the wafer surface are left uncoated, or the film thickness is either too thick or too thin compared to the specified thickness. If areas are left uncoated or the film thickness is too thin, the device layer in that area may be affected by debris. Conversely, if the film thickness is too thick, the laser light may be blocked by the protective film, causing defects in the laser ablation process. Therefore, from the perspective of improving yield, it is necessary to form a protective film with an appropriate thickness, and the film thickness must be inspected in advance.

[0004] One method for inspecting film thickness is to incorporate an absorbent material into the protective film and measure the amount of fluorescence generated when ultraviolet light is applied to the protective film, as described in Patent Document 1. This method makes it possible to determine the film thickness by utilizing the relationship in which the amount of fluorescence increases or decreases depending on the thickness of the protective film. Similarly, Patent Document 2 discloses a method of measuring the thickness of a protective film from the correlation between the thickness of the protective film and the intensity of fluorescence by comparing the thickness before and after application of the protective film to remove the influence of the pattern. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6624919 [Patent Document 2] Japanese Patent Publication No. 2022-178427 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a protective film is continuously irradiated with ultraviolet light, fluorescence fading occurs, in which the amount of fluorescence gradually decreases over time. This fluorescence fading affects the accuracy of the film thickness determined based on the measured fluorescence intensity. However, as exemplified in Patent Documents 1 and 2, conventional protective film inspections do not take fluorescence fading into account when measuring the film thickness.

[0007] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a protective film inspection method and a protective film inspection device that enable highly accurate protective film inspection based on film thickness measurement that takes fluorescence fading into consideration. [Means for solving the problem]

[0008] The present invention employs the following means to solve the above problems and achieve the above objects. (1) A protective film inspection method according to one aspect of the present invention includes: A method for inspecting the coating state of a protective film containing a light absorbing agent coated on a workpiece, comprising: a measuring step of measuring the fluorescence intensity of the fluorescence emitted by the light-absorbing agent when irradiated with excitation light; an inspection step of inspecting the coating state of the protective film based on the fluorescence intensity data obtained in the measurement step; a bleaching step, which is performed before the measurement step, by irradiating the protective film with the excitation light to bleach the light absorbent; It has. According to the protective film inspection method of the above aspect (1), by performing the bleaching step before the measurement step, fluctuation components of the fluorescence intensity can be removed or significantly suppressed in advance. As a result, the thickness of the protective film can be measured based on stable fluorescence intensity in the measurement step. Therefore, highly accurate protective film inspection is possible based on film thickness measurement that takes fluorescence bleaching into account.

[0009] (2) A protective film inspection method according to another aspect of the present invention includes: A method for inspecting the coating state of a protective film containing a light absorbing agent coated on a workpiece, comprising: a main measurement step of irradiating the protective film with excitation light having a wavelength absorbed by the light-absorbing agent, and measuring the fluorescence intensity of the light-absorbing agent emitting light in response to the irradiation of the excitation light, thereby obtaining uncorrected fluorescence intensity data; a preparatory step of measuring the fluorescence intensity of the fluorescence emitted by the light absorbent of the protective film applied to the reference workpiece to obtain correction data under the same fading conditions of the fluorescence intensity, including the application conditions of the protective film and the irradiation conditions of the excitation light, as those of the main measurement step; a correction step of correcting the uncorrected fluorescence intensity data obtained in the main measurement step based on the correction data obtained in the preparation step to obtain corrected fluorescence intensity data; an inspection step of inspecting the coating state of the protective film using the corrected fluorescent intensity data; It has. According to the protective film inspection method of the above aspect (2), the correction step can acquire corrected fluorescence intensity data that reflects fluctuation components of the fluorescence intensity, including the fading conditions. Therefore, the inspection step can inspect the protective film coating state based on the corrected fluorescence intensity data in which the fluctuation components have been removed or significantly reduced. Therefore, the inspection step can inspect the protective film with high accuracy based on film thickness measurements that take fluorescence fading into account.

[0010] (3) In the protective film inspection method described in (2), In the correction step, The corrected fluorescence intensity data A may be obtained for each location along the surface of the workpiece by using the following formula 1 or 2, where A is the corrected fluorescence intensity data, B is the corrected data, C is the uncorrected fluorescence intensity data, and a and b are arbitrary constants both greater than 0.

[0011]

number

[0012] In the case of (3) above, the corrected fluorescence intensity data A can be obtained based on a simple formula, which allows the correction process to be completed in a short time.

[0013] (4) A protective film inspection method according to yet another aspect of the present invention includes: A method for inspecting the coating state of a protective film containing a light absorbing agent coated on a workpiece, comprising: a main measurement step of irradiating the protective film with excitation light having a wavelength absorbed by the light-absorbing agent and measuring the fluorescence intensity of the light-absorbing agent that emits light in response to the irradiation of the excitation light; a preparatory step of measuring the fluorescence intensity of the fluorescence emitted by the light absorbent of the protective film applied to the reference workpiece to obtain correction data under the same fading conditions of the fluorescence intensity, including the application conditions of the protective film and the irradiation conditions of the excitation light, as those of the main measurement step; a threshold distribution calculation step of calculating a threshold distribution along the surface of the workpiece based on the correction data obtained in the preparation step; an inspection step of inspecting the coating state of the protective film by comparing the fluorescence intensity obtained in the main measurement step with the threshold distribution obtained in the threshold distribution calculation step; It has. According to the protective film inspection method of the above aspect (4), the threshold distribution calculation step uses a reference workpiece to calculate a threshold distribution that reflects fluctuation components of the fluorescence intensity, including the bleaching condition. Then, in the inspection step, the fluctuation components contained in the fluorescence intensity obtained in the measurement step can be offset by the fluctuation components contained in the threshold distribution. Therefore, highly accurate protective film inspection is possible based on film thickness measurement that takes fluorescence bleaching into account.

[0014] (5) In the protective film inspection method described in (4), In the threshold distribution calculation step, The threshold distribution may be obtained by obtaining the corrected threshold A1 for each location along the surface of the workpiece using the following (Equation 3), where A1 is the corrected threshold, B1 is the correction data, and a1 is an arbitrary constant greater than 0. A1=a1*B1 (Equation 3) In the case of (5) above, the corrected threshold value can be obtained based on a simple formula, which makes it possible to shorten the time required for the threshold distribution calculation process.

[0015] (6) In the protective film inspection method according to any one of (2) to (5), The reference workpiece may be another workpiece on which a device having the same pattern as the workpiece to be measured in the main measurement step is mounted. In the case of (6) above, in addition to the effects of fading and shading, it is possible to take into account the difference in brightness due to the device pattern.

[0016] (7) A protective film inspection device according to one aspect of the present invention includes: An apparatus for inspecting the coating state of a protective film containing a light absorbing agent that is applied to a workpiece, comprising: an irradiation unit that irradiates the protective film with excitation light having a wavelength that is absorbed by the light absorbent; a measurement unit that measures the fluorescence intensity of the light-absorbing agent that emits light when irradiated with the excitation light; a control unit that controls the irradiation unit and the measurement unit; Equipped with The control unit Before the measurement by the measurement unit, the protective film is irradiated with the excitation light from the irradiation unit to bleach the fluorescence emitted by the light absorbent. According to the protective film inspection device of the above aspect (7), the control unit controls the protective film to bleach the fluorescence emitted from the light absorbent in the protective film before measuring the fluorescence intensity, thereby eliminating or significantly suppressing fluctuations in the fluorescence intensity. This allows the protective film thickness to be measured based on stable fluorescence intensity. Therefore, highly accurate protective film inspection is possible based on film thickness measurements that take fluorescence bleaching into account.

[0017] (8) A protective film inspection device according to another aspect of the present invention includes: An apparatus for inspecting the coating state of a protective film containing a light absorbing agent that is applied to a workpiece, comprising: an irradiation unit that irradiates the protective film with excitation light having a wavelength that is absorbed by the light absorbent; a measurement unit that measures the fluorescence intensity of the light-absorbing agent that emits light upon being irradiated with the excitation light, and obtains uncorrected fluorescence intensity data; a control unit that controls the irradiation unit and the measurement unit and corrects the pre-correction fluorescence intensity data taking into account fading of the fluorescence emitted by the light absorbent; Equipped with The control unit Separately from the main measurement in which the workpiece is the measurement target, a reference workpiece is used instead of the workpiece, and the fading conditions for the fluorescence intensity, including the application conditions of the protective film and the irradiation conditions of the excitation light, are set to be the same as those for the main measurement, and then the fluorescence intensity of the fluorescence emitted by the light absorbent of the protective film applied to the reference workpiece is measured to obtain correction data; The uncorrected fluorescence intensity data obtained in the main measurement is corrected based on the correction data. According to the protective film inspection device of the above aspect (8), it is possible to obtain corrected data that reflects fluctuation components of the fluorescence intensity, including the fading condition, using a reference workpiece. Therefore, when inspecting the coating condition of the protective film formed on the workpiece, it is possible to inspect the coating condition of the protective film based on corrected fluorescence intensity data in which the fluctuation components have been removed or significantly reduced. Therefore, highly accurate protective film inspection is possible based on film thickness measurement that takes fluorescence fading into account.

[0018] (9) A protective film inspection device according to yet another aspect of the present invention includes: An apparatus for inspecting the coating state of a protective film containing a light absorbing agent that is applied to a workpiece, comprising: an irradiation unit that irradiates the protective film with excitation light having a wavelength that is absorbed by the light absorbent; a measuring unit that measures the fluorescence intensity of the light-absorbing agent that emits light upon being irradiated with the excitation light to obtain fluorescence intensity data; a control unit that controls the irradiation unit and the measurement unit, sets a threshold distribution that takes into account fading of the fluorescence emitted by the light absorbent, and inspects the coating state of the protective film; Equipped with The control unit Separately from the main measurement in which the workpiece is the measurement target, a reference workpiece is used instead of the workpiece, and the fading conditions for the fluorescence intensity, including the application conditions of the protective film and the irradiation conditions of the excitation light, are set to be the same as those for the main measurement, and then the fluorescence intensity of the fluorescence emitted by the light absorbent of the protective film applied to the reference workpiece is measured to obtain correction data; setting the threshold distribution along the surface of the workpiece based on the correction data; The protective film is inspected by comparing the fluorescence intensity data obtained in the main measurement with the threshold distribution. According to the protective film inspection device of the above aspect (9), a reference workpiece can be used to set a threshold distribution that reflects fluctuation components of the fluorescence intensity, including the fading condition. When inspecting the coating condition of the protective film formed on the workpiece, the fluctuation components contained in the fluorescence intensity data obtained by the actual measurement can be offset by the fluctuation components contained in the threshold distribution. Therefore, highly accurate protective film inspection is possible based on film thickness measurement that takes fluorescence fading into account.

[0019] (10) In the protective film inspection device according to any one of (7) to (9) above, the following may be performed: The irradiation range of the excitation light and the measurement field of view range of the excitation light are moved spirally or concentrically on the workpiece while being overlapped with each other on the workpiece, The control unit controls the relative positions of the workpiece, the irradiation unit, and the measurement unit. In the case of (10) above, the closer to the radial center of the spiral or concentric circle, the slower the peripheral speed of the excitation light when scanning, resulting in a greater degree of fading than at positions on the periphery. By using the same scanning control during inspection every time, the fading tendency can be made the same for all positions.

[0020] (11) In the protective film inspection device according to any one of (7) to (9) above, the following may be performed: The irradiation range of the excitation light and the measurement field of view range of the excitation light are moved linearly on the workpiece while being overlapped with each other on the workpiece, The control unit controls the relative positions of the workpiece, the irradiation unit, and the measurement unit. In the case of (11) above, the entire surface of the protective film is scanned by performing linear scanning multiple times. In this case, if scanning is repeated in only one direction, the same fading tendency occurs at every position on the entire surface. On the other hand, if forward and backward scanning is repeated, the fading pattern differs between the forward and backward positions. In either case, by using the same scanning control for each inspection, the fading tendency can be made uniform across the entire surface.

[0021] (12) In the protective film inspection device according to any one of (7) to (9), The measurement unit may include any one of a photomultiplier tube, a line sensor camera, an area sensor camera, and a spectroscope. In the case of (12) above, if a photomultiplier tube is used as the measurement unit, weak fluorescence can be amplified and captured. Alternatively, if a line sensor camera is used as the measurement unit, the workpiece can be moved linearly in one direction to acquire fluorescence from the entire surface. Alternatively, if an area sensor camera is used as the measurement unit, coaxial epi-illumination or ring illumination can be suitably used. Furthermore, if a spectroscope is used as the measurement unit, the intensity (spectrum) for each wavelength can be measured. [Effects of the Invention]

[0022] According to the protective film inspection method and protective film inspection device according to the above aspects of the present invention, when inspecting a protective film, highly accurate film thickness measurement taking into account fluorescence fading becomes possible. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a perspective view showing a configuration of a protective film inspection device according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram illustrating the first embodiment, and is a graph illustrating the relationship between the irradiation time of ultraviolet light on the protective film and the intensity of fluorescent light. [Figure 3] 5A to 5C are diagrams illustrating a fading step in the protective film inspection method according to the first embodiment. [Figure 4] FIG. 10 is a diagram showing a continuation of the protective film inspection method according to the first embodiment, illustrating the main measurement performed after the fading step. [Figure 5] 4 is a flowchart of a protective film inspection method according to the first embodiment. [Figure 6] 10A to 10C are diagrams illustrating a protective film inspection method according to a second embodiment of the present invention. [Figure 7] 10A and 10B are diagrams illustrating a case where a coating defect is detected by comparing the same pattern on the wafer surface after the influence of fading has been removed by the protective film inspection method according to the second embodiment. [Figure 8] FIG. 10 is a diagram showing a case where the protective film is spirally scanned by the protective film inspection device according to the third embodiment of the present invention, and is a plan view of the protective film as seen from above. [Figure 9] 10A and 10B are diagrams illustrating a protective film inspection method according to the third embodiment, in which (a) is an image for correction, and (b) is an actual measurement image before correction. [Figure 10] 10A and 10B are diagrams illustrating a protective film inspection method according to the third embodiment, in which (a) is a main measurement image before correction, (b) is a main measurement image after correction, and (c) is a main measurement image after binarization. [Figure 11] 10 is a flowchart of a protective film inspection method according to the third embodiment. [Figure 12]10A and 10B are diagrams illustrating a protective film inspection method according to a fourth embodiment of the present invention, in which (a) is a main measurement image before correction, (b) is a threshold distribution image, and (c) is a main measurement image after binarization. [Figure 13] 10 is a flowchart of a protective film inspection method according to the fourth embodiment. [Figure 14] 10A and 10B are diagrams showing modified examples of the spiral scanning mode in the third embodiment, in which (a) shows a case where scanning is performed linearly in one direction, and (b) shows a case where scanning is performed in a linear, reciprocating manner. [Figure 15] FIG. 10 is a perspective view showing a modified example of the protective film forming apparatus according to the second to fourth embodiments, in which the measurement unit moves linearly and the wafer is rotated around the θ axis. DETAILED DESCRIPTION OF THE INVENTION

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A protective film inspection method and a protective film inspection device according to embodiments of the present invention and their modified examples will be described below with reference to the drawings.

[0025] [First embodiment] First, a first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic diagram showing the configuration of a protective film inspection device according to the first embodiment. The protective film inspection device of this embodiment is provided as part of a laser processing device (not shown) for manufacturing semiconductors, for example. This protective film inspection device is placed on a base LB on the loader side of the laser processing device as shown in Fig. 1, but the protective film inspection device may also be placed on a base on the processing side, if necessary.

[0026] The wafer W, which is the workpiece, has a substrate made of a semiconductor material that is circular in plan view and a device layer formed on the upper surface of the substrate. The upper surface of the device layer of the wafer W is covered with a protective film p to protect the device layer from debris generated during laser ablation processing (hereinafter simply referred to as "processing"), which is performed after protective film inspection. The protective film p is a water-soluble resin film that is washed away along with the debris after processing. The protective film p is inspected by a protective film inspection device for coating conditions such as whether there are any areas that are not coated or whether the film thickness is abnormal. In other words, if there are any areas that are not coated or if the film thickness is too thin, the device layer in that area may be affected by debris, and therefore a "protective film abnormality" is determined. Conversely, if the film thickness is too thick, the protective film p may block the laser light during processing, which may result in processing defects, and therefore a "protective film abnormality" is also determined in this case. If it is determined that "there is an abnormality in the protective film", the wafer W is not subjected to processing, and the protective film p is washed off once, and then the protective film p is recoated by spin coating or the like, and the wafer W is re-inspected.

[0027] The protective film p contains a predetermined amount of light-absorbing agent, and when irradiated with ultraviolet light (an example of excitation light) from the outside, the light-absorbing agent that receives the ultraviolet light emits fluorescence. The intensity of this fluorescence (hereinafter referred to as "fluorescence intensity") is determined mainly by the illumination intensity of the ultraviolet light, the irradiation time of the ultraviolet light, and the film thickness of the protective film p. In other words, the higher the illumination intensity, the higher the fluorescence intensity. Similarly, the thicker the protective film p, the greater the amount of light-absorbing agent, and therefore the higher the fluorescence intensity.

[0028] On the other hand, the irradiation time shows a trend as shown in Figure 2. That is, under conditions where the illumination intensity and film thickness are constant, the fluorescence intensity drops significantly after the start of irradiation (irradiation time 0 seconds), and in the example in the figure, it drops to I1 (approximately 60% of the fluorescence intensity at irradiation time 0 seconds) after t1 seconds. In this way, the fluorescence fades significantly immediately after the start of ultraviolet light irradiation, and the fade progresses further as time passes. Because of this fluctuation in fluorescence intensity due to fade, it has been difficult to accurately determine the film thickness of the protective film p using conventional protective film inspection methods.

[0029] In response to this, the inventors have noticed that the bleaching settles down and approaches a constant value after a certain period of irradiation, as shown for example after t1 in Figure 2. In other words, they believe that by ensuring a sufficient irradiation time of UV light, bleaching can be saturated and the fluctuation components of the fluorescence intensity can be removed. Furthermore, when UV irradiation is stopped, the fluorescence intensity returns to zero, but during this time, the amount of fluorescence gradually recovers. This fluorescence recovery can be confirmed by the fact that the fluorescence intensity measured when UV irradiation is resumed is slightly higher than the final fluorescence intensity measured immediately before UV irradiation was stopped. However, because this fluorescence recovery occurs very slowly over several hours, the shorter the period during which UV irradiation is stopped, the less the fluorescence recovers. Therefore, if UV irradiation is stopped for a short period of time, the fluorescence intensity when UV irradiation is resumed will be the same as the fluorescence intensity at the time of the previous irradiation stop. Because of this tendency in fluorescence recovery, once bleaching has occurred, the bleaching effect can be maintained even if UV irradiation is temporarily stopped, which has the advantage that fluctuations in fluorescence intensity when UV light is applied again can be prevented during the measurement process. Based on these findings, the inventors have completed the protective film inspection method and protective film inspection apparatus of the present invention. First, the overall configuration of the protective film inspection apparatus will be described.

[0030] The protective film inspection device shown in FIG. 1 includes an irradiation unit 10, a detection unit (light receiving unit) 30, a position adjustment unit 40, and a control unit 50. The irradiation unit 10 includes a light source 11 , a lens 12 , and an excitation filter 13 . A light source 11 emits ultraviolet light. The ultraviolet light emitted from the light source 11 is converted into approximately parallel light by a lens 12. The light that passes through the lens 12 further passes through an excitation filter 13 to be limited to a specific excitation wavelength, and is then irradiated from obliquely above onto a protective film p on a wafer W. Note that the ultraviolet light irradiation form shown in FIG. 1 is one example, and other forms may be used instead as necessary. That is, other forms such as coaxial epi-illumination and ring illumination may also be used.

[0031] Although not shown, in the case of coaxial epi-illumination, a detector is placed above the wafer W via a half mirror. Lenses are placed between the half mirror and the detector and between the half mirror and the wafer W. A light source is placed to the side of the half mirror via another lens. In this coaxial epi-illumination, ultraviolet light emitted isotropically from the light source is first collimated by a lens and then sent to the half mirror. The ultraviolet light is reflected by the half mirror, changes direction, and heads toward the wafer W. The light then passes through a lens along the way to be focused and then irradiated onto the protective film p on the wafer W. Next, in the case of receiving fluorescence using this coaxial epi-illumination, the fluorescence emitted from the protective film p in response to the ultraviolet light first passes through a lens on its way to the half mirror to be collimated. This collimated fluorescence then passes through the half mirror and is focused by another lens (a focusing lens) before being received by the detector. On the other hand, when a ring illumination is used as the irradiation unit 10, a condenser lens is placed coaxially in the central space of the ring illumination that emits ultraviolet light. Then, the fluorescence emitted from the protective film p in response to the ultraviolet light irradiated from the ring illumination is received by a detector placed opposite the protective film p with the condenser lens interposed therebetween.

[0032] Returning to the explanation of FIG. 1 , the position adjustment unit 40, upon receiving instructions from the control unit 50, adjusts the horizontal relative positions between the irradiation unit 10 and the detection unit 30 and the turntable 44, as well as the rotation angle of the turntable 44, in order to irradiate a desired position on the protective film p with ultraviolet light emitted from the irradiation unit 10 while observing the fluorescence intensity of the fluorescence emitted from the protective film p with the detection unit (measurement unit) 30. This position adjustment unit 40 makes it possible to scan the protective film p with ultraviolet light in any of a spiral, concentric, or linear manner (unidirectional scanning or reciprocating scanning). Note that in this embodiment, a case will be described in which the positions of the irradiation unit 10 and the detection unit 30 are fixed, and then the position adjustment unit 40 rotates and moves the turntable 44 in the horizontal direction.

[0033] The position adjustment unit 40 includes a Y-axis position adjustment unit 41, an X-axis position adjustment unit 42, a θ-axis angle adjustment unit 43, and a turntable 44. The Y-axis position adjustment unit 41 includes a Y-axis moving base 41a, a pair of guide rails 41b supporting the Y-axis moving base 41a on a base LB, a ball screw 41c arranged on the base LB parallel to the guide rails 41b and rotatably supported about its central axis, and a servo motor 41d for driving the ball screw 41c. The ball screw 41c is threadedly engaged with a female threaded hole (not shown) formed on the underside of the Y-axis moving base 41a. According to the Y-axis position adjustment unit 41, the ball screw 41c rotates when the servo motor 41d is rotated. As a result, the Y-axis moving base 41a, which has the female threaded hole threadedly engaged with the ball screw 41c, moves horizontally along the Y-axis. The control unit 50 appropriately adjusts the amount of rotation of the servo motor 41d to precisely adjust the amount of movement of the Y-axis moving base 41a along the Y-axis, i.e., the position of the turntable 44 along the Y-axis.

[0034] The X-axis position adjustment unit 42 includes an X-axis moving base 42a, a pair of guide rails 42b that support the X-axis moving base 42a on the Y-axis moving base 41a, and a linear motor 42c that is arranged on the Y-axis moving base 41a so as to be parallel to the guide rails 42b and that moves the X-axis moving base 42a along the X-axis. The X-axis position adjustment unit 42 moves the X-axis moving base 42a, which is supported by the guide rails 42b so as to be movable in the X-axis direction, along the X-axis using the linear motor 42c, thereby precisely adjusting the amount of movement of the X-axis moving base 42a along the X-axis, i.e., the position of the turntable 44 along the X-axis.

[0035] The θ-axis angle adjustment unit 43 has a turntable 44, a shaft (not shown) that is erected on the X-axis direction moving base 42a and pivotally supports the turntable 44, and a servo motor (not shown) that rotates the shaft about a vertical axis (about the Z axis). With this θ-axis angle adjustment unit 43, the control unit 50 rotates the servo motor about the Z axis, thereby precisely adjusting the rotation angle of the turntable 44. The turntable 44 is a circular table that can rotate freely around a vertical axis passing through its center. The turntable 44 can suction-fix a wafer W placed on its upper surface. The control unit 50 controls the linear motor 42c and the servo motor 41d, so that the turntable 44 can be positioned with high precision in the Y-axis direction and the X-axis direction. Furthermore, the control unit 50 controls the servo motor of the θ-axis angle adjustment unit 43, so that the θ-axis angle of the turntable 44 can be positioned with high precision.

[0036] The detection unit 30 includes a detector 31 , a lens 32 , and a fluorescence filter 33 . The detector 31 can be selected from an area sensor camera, a line sensor camera, a photomultiplier tube, a spectroscope, or the like, depending on the light receiving method. An area sensor camera is a camera with a sensor in which pixels are arranged two-dimensionally, and is suitable for both coaxial epi-illumination and ring illumination. The line sensor camera is a camera having a sensor with pixels arranged one-dimensionally, and captures an image of the entire surface of the protective film p by linearly moving the wafer W in one direction. Bar lighting is suitable as lighting to be combined with the line sensor camera. A photomultiplier tube is a photodetector that can amplify and capture weak light. Unlike the two cameras mentioned above, a photomultiplier tube measures only one spot. Therefore, spot lighting is suitable for use in combination with this. A spectroscope is a detector that can measure the intensity (spectrum) of each wavelength. Like a photomultiplier tube, a spectroscope also measures only one spot. Therefore, spot lighting is suitable for use in combination with it.

[0037] The fluorescent filter 33 limits the light to a wavelength suitable for observation when transmitting the fluorescent light emitted from the protective film p in response to irradiation with ultraviolet light. The light with this limited wavelength is collected by the lens 32 and then received by the detector 31.

[0038] The control unit 50 controls the irradiation unit 10, the detection unit 30, and the position adjustment unit 40. That is, the control unit 50 controls the irradiation unit 10 and the position adjustment unit 40 to perform an irradiation step in which a desired position on the protective film p is irradiated with ultraviolet light of a wavelength absorbed by the light-absorbing agent. The control unit 50 also controls the detection unit 30 and the position adjustment unit 40 to perform a measurement step in which the fluorescence intensity of the light-absorbing agent that emits light in response to irradiation with ultraviolet light is measured. The control unit 50 also performs an inspection step itself to inspect at least one of the presence or absence and thickness of the protective film p based on the fluorescence intensity data obtained in the measurement step. Furthermore, the control unit 50 controls the irradiation unit 10 and the position adjustment unit 40 to perform a bleaching step prior to the measurement step in which ultraviolet light is irradiated onto the protective film p to bleach the light-absorbing agent.

[0039] A protective film inspection method using the protective film inspection device having the above-described configuration will be described with reference to Figs. 3 to 5. Fig. 3 is a diagram illustrating the fading step of the protective film inspection method, with the steps progressing in the order of (a), (b), ..., (c). Fig. 4 is a diagram illustrating the main measurement performed after the fading step, with the steps progressing in the order of (a), (b), ..., (c). Fig. 5 is a flowchart of the protective film inspection method. 5, the protective film inspection method of this embodiment includes a fading step S1 that is performed subsequent to a protective film application step S0, a measurement step S2 that is performed subsequent to the fading step S1, and an inspection step S3 that is performed subsequent to the measurement step S2. The fading step S1, the measurement step S2, and the inspection step S3 are performed under the control of the control unit 50.

[0040] First, prior to carrying out the protective film inspection method, in a protective film application step S0, a protective film p made of a water-soluble resin agent is formed on the surface of the device layer d of the wafer W by a coating method such as spin coating. A predetermined amount of light absorbing agent is blended in the protective film p. Note that a coating method other than spin coating may also be used to form the protective film p.

[0041] In the bleaching step S1, as shown in FIG. 3, the wafer W is divided into four circumferential areas around its central axis, and each of these four areas is irradiated with ultraviolet light from the irradiation unit 10 for a predetermined time (e.g., approximately 15 seconds). Specifically, the first ultraviolet light irradiation is performed with the turntable rotation temporarily stopped. After the irradiation, the turntable is rotated 90° and temporarily stopped, and then a second ultraviolet light irradiation is performed. The turntable is then rotated another 90° and temporarily stopped, and then a third ultraviolet light irradiation is performed. The turntable is then rotated another 90° and temporarily stopped, and then a fourth ultraviolet light irradiation is performed. During this process, the irradiation time per wafer W is 15 seconds x 4 areas, for a total of 60 seconds. Note that the irradiation time per area is set to 15 seconds here, but is not limited to 15 seconds. It can be set to any time sufficient to saturate the bleaching, for example, between 10 and 30 seconds.

[0042] Here, if the protective film p of the wafer W is divided into four areas, each area will have a sector shape consisting of two straight lines extending radially from the center of the wafer W and perpendicular to each other, and one circular arc. Meanwhile, the UV light irradiation area is circular, indicated by the symbol ul. Therefore, while one of the four areas is being irradiated with UV light, the other areas adjacent to the irradiation area ul will also be irradiated. In other words, at the four adjacent portions of the four areas, partial overlap occurs due to the overflow of the irradiation area ul. The irradiation time at these overlapping areas is longer than at other areas. However, as shown in Figure 2, once bleaching saturates, the relative fluorescence intensity remains almost unchanged even if the irradiation time is extended. Furthermore, while the ultraviolet light is being applied from one irradiated area to the next, the irradiated area is in a non-irradiated state, but as mentioned above, it takes several hours for the color to return to its original state once the fading has saturated. As a result, a uniformly saturated bleaching distribution is formed across the entire surface without any localized unevenness in bleaching, as shown in Figure 3(c). Furthermore, once a bleaching distribution is formed, fluorescence recovery tends to proceed very slowly even after the UV light irradiation is stopped, so it is possible to proceed with the inspection as if there is no fluorescence recovery.

[0043] In the measurement step S2, which is carried out immediately following the bleaching step S1, the wafer W is divided into four areas in the circumferential direction around its central axis, as shown in Fig. 4, and the fluorescence intensity is measured for each of these four areas by the detection unit 30 while irradiating them with ultraviolet light. Note that in Fig. 4, the circle indicated by the symbol ul indicates the irradiation range of the ultraviolet light, and the field of view va, which will be described later, is included within this irradiation range.

[0044] After each area is set, the turntable is stopped from rotating and a first fluorescence intensity measurement is performed. The turntable is then rotated 90° and stopped for a second fluorescence intensity measurement. The turntable is then rotated another 90° and stopped for a third fluorescence intensity measurement. The turntable is then rotated another 90° and stopped for a fourth fluorescence intensity measurement. To measure the fluorescence intensity of each area, the detector 30 captures an image of the field of view va in the square region (more specifically, the square imaging range) indicated by the symbol va in FIG. 4, and measures the fluorescence intensity distribution within that range. Because the fading of the fluorescence intensity of the protective film p in each of these four fields of view va has already been saturated by the fading step S1, measurement results are obtained that are free of fluorescence intensity variations associated with fading.

[0045] In the inspection step S3 following the measurement step S2, the actual measurement image is binarized to obtain a binarized image, using the previously acquired correlation between the thickness of the protective film p and the fluorescence intensity as the criterion for determining whether the currently measured thickness distribution of the protective film p is within an appropriate thickness range. Based on this binarized image, if the fluorescence intensity of the entire surface is within the fluorescence intensity range, the wafer W is deemed to have passed, and the wafer W is sent to the next processing step. On the other hand, if even a portion of the fluorescence intensity of the entire surface is outside the fluorescence intensity range, the wafer W is deemed to have failed, and instead of being sent to the next process, the wafer W is sent to the protective film coating step S0, where the protective film p is recoated. After recoating, the wafer W is again subjected to the fading step S1, measurement step S2, and inspection step S3.

[0046] As described above, the protective film inspection method of this embodiment is a method for inspecting the coating state of a protective film p containing a light absorbent that is coated on a wafer (workpiece) W, and includes a measurement step S2 in which the fluorescence intensity of the fluorescence emitted by the light absorbent that has been irradiated with excitation light is measured, an inspection step S3 in which the coating state of the protective film p is inspected based on the fluorescence intensity data obtained in the measurement step S2, and a fading step S1 in which, prior to the measurement step S2, the protective film p is irradiated with excitation light to cause the light absorbent to fade. The protective film inspection device of this embodiment, which executes this protective film inspection method, is an apparatus for inspecting the coating state of a protective film p containing a light absorbent that is coated on a wafer W, and includes an irradiation unit 10 that irradiates the protective film p with ultraviolet light, which is excitation light of a wavelength absorbed by the light absorbent, a detection unit 30 that measures the intensity of fluorescence emitted from the light absorbent that emits light in response to irradiation with ultraviolet light, and a control unit 50 that controls the irradiation unit 10 and the detection unit 30. The control unit 50 bleaches the fluorescence emitted from the light absorbent by irradiating the protective film p with ultraviolet light from the irradiation unit 10 before measurement by the detection unit 30. According to these protective film inspection methods and protective film inspection devices, by performing the fading step S1 before the measurement step S2, it is possible to eliminate or significantly suppress fluctuations in the fluorescence intensity in advance. This allows the film thickness of the protective film p to be measured based on stable fluorescence intensity in the measurement step S2. Therefore, highly accurate protective film inspection is possible based on film thickness measurements that take fluorescence fading into account.

[0047] [Second embodiment] Next, a second embodiment of the present invention will be described below with reference to FIGS. Fig. 6 is a diagram illustrating a protective film inspection method according to this embodiment. Fig. 7 is a diagram illustrating a case where a coating defect is detected by comparing the same pattern on the surface of a wafer W after the influence of fading has been removed by the protective film inspection method according to this embodiment. Note that the protective film inspection apparatus used in the protective film inspection method of this embodiment has almost the same apparatus configuration as the first embodiment shown in Fig. 1, so the same product number is basically used and the differences will be mainly described.

[0048] In the first embodiment, the fading of the protective film p applied to the wafer W is saturated before the actual measurement. In contrast, in this embodiment, as shown in FIG. 6(a), a reference workpiece SW is first prepared, and a protective film p is formed on the reference workpiece SW under the same application conditions as the actual measurement. Then, ultraviolet light is irradiated onto the reference workpiece SW under the same irradiation conditions as the actual measurement to obtain data on the fading unevenness, which is used as correction data. Next, as shown in FIG. 6(b), ultraviolet light is irradiated onto the wafer W to be measured under the same irradiation conditions as the reference workpiece SW to measure the fluorescence intensity distribution. Finally, the correction data obtained from the reference workpiece SW is applied to the fluorescence intensity distribution obtained in the actual measurement to offset the fading unevenness, and the corrected actual measurement result shown in FIG. 6(c) is obtained. Details are explained again below.

[0049] First, the process begins with acquiring correction data using a reference work SW. FIG. 6(a) illustrates a case where a mirror wafer without a device layer d is used as the reference work SW. In this embodiment, the fading conditions for the fluorescence intensity, including the conditions for applying the protective film p to the reference work SW and the conditions for irradiating it with ultraviolet light, are set to the same as the fading conditions for the actual measurement process, and then a preparatory process is performed in which the fluorescence intensity is measured to obtain correction data. That is, in this preparatory process, the reference work SW with the protective film p formed thereon is first placed on the turntable 44 of the protective film inspection device shown in FIG. 1.

[0050] Next, the reference work SW is divided into four areas circumferentially around its central axis, and the four areas are irradiated with ultraviolet light from the irradiation unit 10 while the fluorescence intensity is measured by the detection unit 30. That is, the rotation of the turntable 44 is temporarily stopped while irradiating with ultraviolet light, and a first fluorescence intensity measurement is performed, after which the turntable 44 is rotated 90° and the rotation is temporarily stopped, and a second fluorescence intensity measurement is performed while irradiating with ultraviolet light, and after which the turntable 44 is rotated another 90° and the rotation is temporarily stopped, and a third ultraviolet light irradiation is performed while irradiating with ultraviolet light, and after the irradiation, the turntable 44 is rotated another 90° and the rotation is temporarily stopped, and a fourth fluorescence intensity measurement is performed while irradiating with ultraviolet light.

[0051] The fluorescence intensity distribution obtained in this manner is shown in Figure 6(a). In this figure, there are four linear areas passing through the center of the reference work SW, where strong fading occurs in the horizontal and vertical directions of the page. These are caused by the exposure of the UV light that spilled over into the adjacent areas when each of the four areas was irradiated with UV light. Thus, a roughly X-shaped fading unevenness occurs in the fluorescence intensity on the surface of the protective film p, and similar fading unevenness will occur every time in the actual measurement that follows. In addition to this fading unevenness, the fluorescence intensity distribution measured on the reference work SW also reflects other fluctuation components, such as shading, which is brightness unevenness caused by the optical system. Naturally, these fluctuation components will also occur every time in the actual measurement that follows. The above is the preparation process, and the fluorescence intensity distribution measured on the reference work SW can be used as correction data that reflects all fluctuation components that also occur in the actual measurement.

[0052] Following the preparation step, a main measurement step is performed on the wafer W, which is the workpiece. That is, similar to the procedure performed on the reference workpiece SW in the preparation step, the wafer W on which the protective film p is formed is divided into four areas in the circumferential direction around its central axis, and the fluorescence intensity is measured by the detection unit 30 while irradiating each of these four areas with ultraviolet light from the irradiation unit 10. These four areas may be the same as those set in the preparation step. In this measurement process, the rotation of the turntable 44 is stopped and ultraviolet light is irradiated while a first fluorescence intensity measurement is performed, then the turntable 44 is rotated 90° and the rotation is stopped and ultraviolet light is irradiated while a second fluorescence intensity measurement is performed, then the turntable 44 is rotated another 90° and the rotation is stopped and ultraviolet light is irradiated while a third ultraviolet light irradiation is performed, and after the irradiation, the turntable 44 is rotated another 90° and the rotation is stopped and ultraviolet light is irradiated while a fourth fluorescence intensity measurement is performed. The fluorescence intensity distribution obtained in this way is as shown in Figure 6(b), and contains fluctuation components including the same uneven fading as that measured in the reference work SW.

[0053] Therefore, a correction process is carried out following the main measurement process. In this correction process, the correction data (FIG. 6(a)) previously acquired in the preparation process is used to correct the uncorrected fluorescence intensity data acquired in the main measurement process, to obtain the corrected fluorescence intensity data shown in FIG. 6(c). Specifically, the corrected fluorescence intensity data shown in FIG. 6(c) is A, the correction data shown in FIG. 6(a) is B, and the uncorrected fluorescence intensity data shown in FIG. 6(b) is C, with a and b being arbitrary constants both greater than 0. Then, for each location along the surface of the protective film p of the wafer W, the corrected fluorescence intensity data A is calculated using the following equation 1 or 2:

[0054]

number

[0055] In the inspection process following the correction process, the actual measurement image is binarized to obtain a binarized image, using the previously acquired correlation between the thickness of the protective film p and the fluorescence intensity as the criterion for determining whether the currently measured thickness distribution of the protective film p is within an appropriate thickness range. Based on this binarized image, it is determined whether the fluorescence intensity of the entire surface is within the fluorescence intensity range. As a result, if the fluorescence intensity of the entire surface of the actual measurement image is within the fluorescence intensity range, the wafer W is deemed to have passed, and the wafer W is sent to the next processing step. On the other hand, if even a portion of the fluorescence intensity of the entire surface is outside the fluorescence intensity range, the wafer W is deemed to have failed, and the protective film p is washed off without being sent to the next process, and a protective film p is recoated. After the recoating, the wafer W is again subjected to the actual measurement process, correction process, and inspection process described above.

[0056] As described above, the protective film inspection method of this embodiment is a method for inspecting the coating state of a protective film p containing an absorbent that is coated on a wafer (workpiece) W, and includes the following steps: a main measurement step in which the protective film p is irradiated with ultraviolet light (excitation light) of a wavelength absorbed by the absorbent, and the fluorescence intensity of the fluorescence emitted from the absorbent that emits light in response to the ultraviolet light irradiation is measured to obtain pre-correction fluorescence intensity data; a preparatory step in which the fluorescence intensity of the protective film p coated on a reference work SW is measured to obtain correction data under the same fluorescence intensity fading conditions as those in the main measurement step, including the coating conditions of the protective film p and the irradiation conditions of the ultraviolet light; a correction step in which the pre-correction fluorescence intensity data obtained in the main measurement step is corrected based on the correction data obtained in the preparatory step to obtain corrected fluorescence intensity data; and an inspection step in which the corrected fluorescence intensity data is used to inspect the coating state of the protective film p. The protective film inspection apparatus of this embodiment, which executes this protective film inspection method, is an apparatus for inspecting the coating condition of a protective film p containing a light-absorbing agent coated on a wafer W, and includes an irradiation unit 10 that irradiates the protective film p with ultraviolet light of a wavelength absorbed by the light-absorbing agent, a detection unit 30 that measures the fluorescence intensity of fluorescence emitted from the light-absorbing agent that emits light in response to the ultraviolet light irradiation to obtain pre-correction fluorescence intensity data, and a control unit 50 that controls the irradiation unit 10 and the detection unit 30 and corrects the pre-correction fluorescence intensity data to take into account fading of the light-absorbing agent. Separately from an actual measurement in which the wafer W is the measurement target, the control unit 50 measures the fluorescence intensity of fluorescence emitted from the protective film p coated on a reference work SW that serves as a substitute for the wafer W, while setting the fluorescence intensity fading conditions, including the coating conditions of the protective film p and the irradiation conditions of ultraviolet light, to the same as those in the actual measurement, to obtain correction data, and then corrects the pre-correction fluorescence intensity data obtained in the actual measurement based on the correction data.

[0057] According to these protective film inspection methods and protective film inspection devices, in the inspection process, the protective film p of the wafer W can be inspected based on the corrected fluorescence intensity data in which the fluctuation components have been removed or significantly reduced. Therefore, in the inspection process, highly accurate protective film inspection is possible based on film thickness measurement that takes fluorescence fading into consideration. In particular, this embodiment can correct for fading regardless of the scanning method used when irradiating ultraviolet light and measuring fluorescence intensity. Furthermore, as described above, other fluctuations such as shading can also be simultaneously removed by correction. Therefore, it becomes possible to confirm the pattern formed on the surface of the device layer (pattern formed due to device arrangement, etc.). This allows for the detection of coating defects df by comparing multiple identical patterns, as shown in Figure 7, for example. In other words, in the example of Figure 7, the three devices lined up vertically, surrounded by a bold frame, all have the same pattern, but a coating defect df can be confirmed at the position of one device at the top of the page, which is not present at the positions of the other two devices.

[0058] In comparison with the first embodiment, the second embodiment has the advantage of high throughput and a high S / N ratio because the fading step S1 is unnecessary. On the other hand, the first embodiment has the advantage of not requiring the preparation of correction data using a reference workpiece SW. Therefore, it is preferable to select which of these methods to adopt depending on the inspection purpose and inspection conditions. Furthermore, in the second embodiment, a mirror wafer is used as the reference work SW, but the present invention is not limited to this. A wafer W identical to that used for the actual measurement, on which a device of the same pattern is mounted, may be separately prepared as a sample and used as the reference work SW. In this case, in addition to the effects of fading and shading, it is possible to reflect the difference in brightness due to the device pattern in the correction data, enabling film thickness inspection to be performed with even higher accuracy.

[0059] [Third embodiment] Next, a third embodiment of the present invention will be described below with reference to FIGS. The configuration of the protective film inspection device used in this embodiment is the same as the device configuration described in FIG. 1, so in the following description, the same components as those in the first embodiment above will be denoted by the same reference numerals, and duplicated description will be omitted.

[0060] In this embodiment, as shown in Fig. 8, a case will be described in which the fluorescence intensity distribution is measured while the field of view (measurement field of view range) va is moved spirally relative to the protective film p. That is, the control unit 50 measures the fluorescence intensity distribution while driving the turntable 44 etc. so that the position of the field of view va of the detection unit 30 moves from the outer circumferential direction toward the center of rotation in the order va1, va2, va3. Note that in Fig. 8, the hatched circular portion indicates the protective film p.

[0061] The control unit 50 controls the irradiation unit 10, the detection unit 30, and the position adjustment unit 40. That is, the control unit 50 controls the irradiation unit 10 and the position adjustment unit 40 to irradiate the reference work SW and the wafer W for actual measurement with ultraviolet light of a wavelength absorbed by the absorbent. The control unit 50 also controls the detection unit 30 and the position adjustment unit 40 to measure the fluorescence intensity of the absorbent that emits light in response to irradiation with ultraviolet light for the reference work SW and the wafer W for actual measurement. The control unit 50 also creates correction data based on the fluorescence intensity data obtained from the reference work SW and corrects the fluorescence intensity data of the wafer W using this correction data. Finally, the control unit 50 also performs an inspection process to inspect at least one of the presence or absence and thickness of a protective film p.

[0062] A protective film inspection method using the protective film inspection device having the above-described configuration will be described with reference to Figs. 9 to 11. In Fig. 9, (a) shows the correction image, and (b) shows the actual measured image before correction. In Fig. 10, (a) shows the actual measured image before correction, (b) shows the actual measured image after correction, and (c) shows the actual measured image after binarization. Fig. 11 shows a flowchart of the protective film inspection method of this embodiment.

[0063] 11, the protective film inspection method of this embodiment includes a protective film application step S1A to a reference workpiece SW, a first measurement step S2A performed subsequent to the protective film application step S1A to the reference workpiece SW, a protective film application step S0 to a wafer for actual measurement performed subsequent to the first measurement step S2A, a second measurement step S3A performed subsequent to the protective film application step S0 to the wafer for actual measurement, an image correction step S4A performed subsequent to the second measurement step S3A, and an inspection step S5A performed subsequent to the image correction step S4A. Of these steps, the first measurement step S2A, the second measurement step S3A, the image correction step S4A, and the inspection step S5A are executed under the control of the control unit 50.

[0064] First, prior to measuring the wafer W for main measurement, a protective film p is formed on the reference work SW, and a correction image (correction data) is acquired. That is, in the protective film coating step S1A on the reference work SW, the protective film p is formed under the same conditions as in the protective film coating step S0 on the wafer W for actual measurement that follows. Specifically, a protective film p made of a water-soluble resin agent is formed on the surface of the reference work SW by a coating method such as spin coating. A predetermined amount of light-absorbing agent is blended in the protective film p. Note that a coating method other than spin coating may also be used to form the protective film p.

[0065] In the subsequent first measurement step S2A, as shown in FIG. 8, the reference workpiece SW is scanned spirally from its outer periphery toward its center at a constant rotational speed to measure the fluorescence intensity distribution over the entire surface of the protective film p. Based on this measurement result, a correction image (correction data) is output, as shown in FIG. 9(a). As the hatching density increases toward the center in FIG. 9(a), the tendency for discoloration to fade becomes stronger toward the radially inner side of the reference workpiece SW, with the degree of discoloration being greatest at the center. This discoloration distribution is formed by the difference in peripheral speed that occurs when ultraviolet light is irradiated spirally. That is, when scanning the entire surface of the protective film p, the faster peripheral speed on the outer periphery shortens the ultraviolet light irradiation time, resulting in a smaller degree of discoloration. On the other hand, the relatively slower peripheral speed on the inner periphery lengthens the ultraviolet light irradiation time, resulting in a larger degree of discoloration. This fluorescence intensity distribution occurs exactly the same when measuring the wafer W for actual measurement. Therefore, the measurement results of the reference workpiece SW are used as correction data to correct the measurement results of the wafer W for main measurement.

[0066] That is, first, in a protective film coating step S0 on the wafer W for actual measurement, a protective film p is coated and formed under the same conditions as those on the reference workpiece SW. Next, in the second measurement step S3A, as shown in FIG. 8, the fluorescent intensity distribution over the entire surface of the protective film p is measured by spirally scanning the wafer W from its outer periphery toward its center at a constant rotational speed. Here, the measurement conditions, including the peripheral speed, are the same as those for the reference workpiece SW. Then, based on the measurement results, the actual measurement image shown in FIG. 9(b) is obtained. As the hatching in FIG. 9(b) becomes darker toward the center, the tendency for fading to become stronger toward the radially inner side of the wafer W, with the degree of fading being strongest at the center. In other words, the same fading tendency as confirmed in the correction data is occurring, and the coating film defect df is mixed in with it.

[0067] Therefore, the actual measurement image is corrected in the subsequent image correction step S4A. That is, the previously acquired correction data is applied to the actual measurement image before correction shown in Fig. 10(a) to remove the fading tendency, and the corrected actual measurement image shown in Fig. 10(b) is obtained. Specifically, first, let A be the corrected fluorescence intensity data in the corrected actual measurement image, B be the corrected data obtained in the first measurement step S2A, and C be the uncorrected fluorescence intensity data in the actual measurement image before correction, and let a and b be arbitrary constants both greater than 0. Then, for each location along the surface of the wafer W, corrected fluorescence intensity data A is obtained using Equation 1 or 2 below. For this correction, each correction image shown in the square frame in FIG. 10 has position information on the surface of the reference workpiece SW, and the actual measurement image within the same square frame has position information on the surface of the wafer W. After the position information for both is correctly matched, correction is performed at each position to obtain individual corrected images.

[0068]

number

[0069] In this embodiment, as shown in Figure 10, an example is shown in which the surface of the protective film p is divided into multiple regions, and each region is first corrected and then finally combined into a single image.However, this is not the only possible form.Small images of the entire region may first be combined to obtain a single actual measurement image, and then the same single correction image may be used to perform correction in one go.

[0070] In the inspection step S5A following the image correction step S4A, a determination is made as to whether the currently measured thickness distribution of the protective film p is within the appropriate thickness range based on the previously acquired correlation between the thickness of the protective film p and the fluorescence intensity. Specifically, the corrected measurement image shown in Figure 10(b) is binarized into two categories: those with fluorescence intensity that correspond to the appropriate thickness range and those that do not, to obtain the binarized image shown in Figure 10(c). This binarized image allows the detection of coating defects df. If there are no coating defects df or if they are located in negligible positions, the wafer W is deemed to have passed, and is sent to the next processing step. On the other hand, if a coating defect df that will cause problems in the next processing step is detected, the wafer W is deemed to have failed, and the protective film p is washed away without being sent to the next process, and the protective film p is recoated again. After recoating, the wafer W is again subjected to the second measurement step S3A, image correction step S4A, and inspection step S5A described above.

[0071] As described above, the protective film inspection method of this embodiment is a method for inspecting the coating state of a protective film p containing an absorbent coated on a wafer W, and includes a second measurement process (main measurement process) S3A in which excitation light of a wavelength absorbed by the absorbent is irradiated onto the protective film p, and the fluorescence intensity of the fluorescence emitted from the absorbent that emits light in response to the irradiation of the excitation light is measured to obtain pre-correction fluorescence intensity data; a preparation process (protective film application process S1A to reference workpiece and first measurement process S2A) in which the fluorescence intensity fading conditions, including the coating conditions of the protective film p and the irradiation conditions of the excitation light, are set to the same as those in the second measurement process S3A, and correction data is obtained by measuring the fluorescence intensity of the fluorescence emitted from the protective film p coated on the reference workpiece SW; an image correction process (correction process) S4A in which the pre-correction fluorescence intensity data obtained in the second measurement process S3A is corrected based on the correction data obtained in the preparation process to obtain corrected fluorescence intensity data; and an inspection process S5A in which the corrected fluorescence intensity data is used to inspect the coating state of the protective film p.

[0072] A protective film inspection device for performing this protective film inspection method is a device for inspecting the coating state of a protective film p containing a light-absorbing agent, and includes an irradiation unit 10 that irradiates the protective film p with excitation light of a wavelength absorbed by the light-absorbing agent, a detection unit 30 that measures the fluorescence intensity of fluorescence emitted from the light-absorbing agent that emits light in response to the irradiation of the excitation light to obtain pre-correction fluorescence intensity data, and a control unit 50 that controls the irradiation unit 10 and the detection unit 30 and corrects the pre-correction fluorescence intensity data taking into account fading of the fluorescence emitted from the light-absorbing agent. Separately from a second measurement step (main measurement step) S3A in which a wafer W is used as the measurement object, the control unit 50 measures the fluorescence intensity of the protective film p coated on a reference work SW that serves as a substitute for the wafer W under the same fading conditions for the fluorescence intensity as in the second measurement step S3A, including the coating conditions of the protective film p and the irradiation conditions of the excitation light, to obtain correction data, and corrects the pre-correction fluorescence intensity data obtained in the second measurement step S3A based on the correction data.

[0073] According to these protective film inspection methods and protective film inspection devices, in the inspection step S5A, it is possible to inspect the coating state of the protective film p on the wafer W based on the corrected fluorescence intensity data in which the fluctuation component has been removed or significantly reduced. Therefore, in the inspection step S5A, highly accurate protective film inspection is possible based on film thickness measurement that takes fluorescence fading into consideration. In this embodiment, a mirror wafer is used as the reference work SW, but the present invention is not limited to this. A wafer W identical to that used for the actual measurement and having a device mounted thereon may be separately prepared as a sample and used as the reference work SW. In this case, in addition to the effects of fading and shading, it is possible to reflect the difference in brightness due to the device pattern in the correction data, enabling film thickness inspection to be performed with even higher accuracy.

[0074] [Fourth embodiment] Next, a fourth embodiment of the present invention will be described below with reference to Fig. 12 and Fig. 13. Fig. 12 illustrates a protective film inspection method according to this embodiment, where (a) is a main measurement image before correction, (b) is a threshold distribution image, and (c) is a main measurement image after binarization. Fig. 13 is a flowchart of the protective film inspection method according to this embodiment. This embodiment corresponds to a modification of the third embodiment. That is, while in the third embodiment, correction data is applied to the actual measurement image, in this embodiment, correction data is applied to the threshold value. Furthermore, the protective film inspection device used in this embodiment has the same configuration as the device shown in FIG. 1 described in the first embodiment, with only the control content by the control unit 50 being different. Therefore, the protective film inspection method of this embodiment will be described based on the device configuration shown in FIG. 1.

[0075] 13, the protective film inspection method of this embodiment includes a protective film applying step S1B to a reference workpiece SW, a first measurement step S2B performed subsequent to the protective film applying step S1B to the reference workpiece SW, a threshold distribution calculation step S3B performed subsequent to the first measurement step S2B, a protective film applying step S0 to a wafer W for actual measurement performed subsequent to the threshold distribution calculation step S3B, a second measurement step S4B performed subsequent to the protective film applying step S0 to the wafer W for actual measurement, and an inspection step S5B performed subsequent to the second measurement step S4B. Of these steps, the first measurement step S2B, the threshold distribution calculation step S3B, the second measurement step S4B, and the inspection step S5B are executed as a protective film inspection method under the control of the control unit 50.

[0076] First, prior to measuring the wafer W for main measurement, a protective film p is formed on a reference work SW to obtain a threshold distribution (correction data). That is, in the protective film application step S1B on the reference work SW, the protective film p is formed under the same conditions as in the protective film application step S0 on the wafer W for actual measurement that follows. Specifically, a protective film p made of a water-soluble resin agent is formed on the surface of the reference work SW by a coating method such as spin coating. A predetermined amount of light-absorbing agent is blended in the protective film p. Note that a coating method other than spin coating may also be used to form the protective film p.

[0077] In the subsequent first measurement step S2B, similar to the procedure shown in Figure 8, the reference work SW is spirally scanned from the outer periphery to the center at a constant rotation speed to measure the fluorescence intensity distribution over the entire surface of the protective film p. In the subsequent threshold distribution calculation step S3B, as shown in FIG. 12, threshold data taking into account the fading tendency is calculated based on the measurement results of the previous step. That is, in the third embodiment, the actual measurement image was corrected using the same fixed threshold at each position on the surface of the wafer W. In contrast, in this embodiment, the actual measurement image is not corrected, but the threshold is individually corrected taking into account the fading at each position on the surface of the wafer W. Specifically, the corrected threshold at each position on the surface of the wafer W is set to A1, the correction data is set to B1, and an arbitrary constant greater than 0 is set to a1, and the corrected threshold A1 is obtained for each location along the surface of the wafer W using the following equation 3. In this way, by dividing the surface of the protective film p into multiple regions, correcting the threshold for each region, and finally combining the results into a single image, the corrected threshold image shown in FIG. 12(b) is obtained. Each correction image shown within the square frame in Figure 12 has position information on the surface of the reference work SW, and the threshold distribution image shown within the same square frame has position information on the surface of the wafer W. After the position information of both images is correctly matched, threshold correction is performed at each position to obtain individual corrected threshold images.

[0078] A1=a1*B1 (Equation 3)

[0079] The above steps result in the corrected threshold distribution shown in Fig. 12(b). As shown in the figure, this corrected threshold distribution has a distribution in which the tendency for fading is more strongly reflected toward the inner side in the radial direction of the wafer W, and the degree of fading is most strongly reflected at the center position.

[0080] In the subsequent protective film coating step S0 on the wafer W for actual measurement, a protective film p is coated and formed under the same conditions as those for the reference workpiece SW. Next, in the second measurement step S4B, as shown in FIG. 8, the fluorescence intensity distribution over the entire surface of the protective film p is measured by spirally scanning the wafer W from its outer periphery toward its center at a constant rotation speed. Here, the measurement conditions, including the peripheral speed, are the same as those for the reference workpiece SW. The corrected threshold image data created in the threshold distribution calculation step S3B is then applied to the obtained fluorescence intensity distribution. That is, it is determined for each position on the surface of the wafer W whether or not the fluorescence intensity at that position satisfies the corrected threshold A1 in the corrected threshold image data, and binarization is performed based on the results to obtain the binary image of the actual measurement image shown in FIG. 12(c).

[0081] In the subsequent inspection step S5B, coating defects df are detected using the binarized image ((c) of Figure 12) obtained in the previous step. If there are no coating defects df or if they are located in negligible positions, the wafer W is deemed to have passed, and the wafer W is sent to the next processing step. On the other hand, if a coating defect df that will cause problems in the next processing step is detected, the wafer W is deemed to have failed, and the protective film p is washed away without being sent to the next step, and the protective film p is recoated again. After recoating, the wafer W is again subjected to the second measurement step S4B and inspection step S5B described above.

[0082] As described above, the protective film inspection method of this embodiment is a method for inspecting the coating state of a protective film p containing an absorbent coated on a wafer W, and includes a second measurement process (main measurement process) S4B in which excitation light of a wavelength absorbed by the absorbent is irradiated onto the protective film p and the fluorescence intensity of the fluorescence emitted from the absorbent that emits light in response to the irradiation of the excitation light is measured; a preparation process (protective film application process S1B to reference work SW and first measurement process S2B) in which the fluorescence intensity is measured to obtain correction data while the fluorescence intensity fading conditions, including the coating conditions of the protective film p and the irradiation conditions of the excitation light, are set to the same as those in the second measurement process S4B; a threshold distribution calculation process S3B in which a threshold distribution along the surface of the wafer W is calculated based on the correction data obtained in the preparation process; and an inspection process S5B in which the fluorescence intensity obtained in the second measurement process S4B is compared with the threshold distribution obtained in the threshold distribution calculation process S3B to inspect the coating state of the protective film p.

[0083] Furthermore, a protective film inspection apparatus for carrying out this protective film inspection method is an apparatus for inspecting the coating state of a protective film p containing a light absorbent that is coated on a wafer W, and includes an irradiation unit 10 that irradiates the protective film p with excitation light of a wavelength absorbed by the light absorbent, a detection unit 30 that measures the fluorescence intensity of fluorescence emitted from the light absorbent that emits light in response to the irradiation of the excitation light to obtain fluorescence intensity data, and a control unit 50 that controls the irradiation unit 10 and the detection unit 30, sets a threshold distribution that takes into account fading of the light absorbent, and inspects the coating state of the protective film p. The control unit 50 measures the wafer W. Separately from the second measurement process (main measurement process) S4B, which is the target of determination, a reference work SW, which serves as a substitute for the wafer W, is subjected to the same fluorescence intensity fading conditions as in the second measurement process S4B, including the application conditions of the protective film p and the irradiation conditions of the excitation light, and the fluorescence intensity of the fluorescence emitted from the protective film p applied to the reference work SW is measured to obtain correction data.Based on the correction data, a threshold distribution is set along the surface of the wafer W, and the fluorescence intensity data obtained in the second measurement process S4B is compared with the threshold distribution to inspect the application state of the protective film p.

[0084] According to these protective film inspection methods and protective film inspection devices, in the inspection step S5B, it is possible to inspect the coating state of the protective film p on the wafer W based on the binarized data in which the fluctuation components have been removed or significantly reduced. Therefore, in the inspection step S5B, it is possible to perform highly accurate protective film inspection based on film thickness measurement that takes fluorescence fading into consideration. In this embodiment, a mirror wafer is used as the reference work SW, but the present invention is not limited to this. A wafer W for actual measurement on which a device is mounted may be prepared separately and used as the reference work SW. In this case, in addition to the effects of fading and shading, the difference in brightness due to the device pattern can also be reflected in the threshold distribution, enabling film thickness inspection to be performed with even higher accuracy.

[0085] Although the protective film inspection method and protective film inspection device according to the present invention have been described above as respective embodiments, modifications such as combining these embodiments may be made as needed. In addition, in the first embodiment described above, as shown in FIG. 3, during the fading step S1 of the wafer W, the surface of the protective film p is divided into four parts and irradiated with ultraviolet light. However, the present invention is not limited to this form, and the ultraviolet light may be irradiated in a spiral scanning manner, or in a linear scanning manner.

[0086] Similarly, in the second to fourth embodiments, ultraviolet light was irradiated and the fluorescence intensity was measured while scanning in a spiral manner, but this is not the only possible mode, and scanning may also be performed in a linear manner, for example, as shown in (a) or (b) of Figure 14. Here, Figure 14(a) shows a case where fluorescence intensity is measured while irradiating ultraviolet light linearly in one direction. While irradiating the irradiation area ul with ultraviolet light and measuring the fluorescence intensity in the field of view va, the scanner moves linearly from the bottom to the top of the paper. This linear scan is then performed multiple times to measure the fluorescence intensity over the entire surface of the protective film p, scanning one line at a time from the left edge of the paper to the right edge. In this case, since the scanning direction of each scan line is the same, the same fading tendency is observed at every position. Therefore, correction is possible with a single representative fading image.

[0087] On the other hand, in the case of FIG. 14(b), the ultraviolet light is irradiated linearly, similar to FIG. 14(a), but the scanning is reciprocated vertically. In this case, in the first scan at the left edge of the page, the area above the rectangular frame indicated by the field of view va has already begun to fade due to UV light irradiation, just like the field of view va. On the other hand, in the scan line immediately to the right of this scan line, the area below the rectangular frame indicated by the field of view va has already begun to fade due to UV light irradiation, just like the field of view va. As such, in the case of FIG. 14(b), the fading patterns differ between the forward and backward passes. Therefore, in the second and third embodiments, it is necessary to align the direction of the fading distribution on the reference workpiece SW with the direction of the fading distribution on the wafer W for actual measurement. If it is difficult to align the orientations, multiple correction images aligned with the scanning direction may be prepared and the one that matches the scanning direction may be selected for correction. Alternatively, if the direction of the scanning back and forth path is symmetrical with respect to a center line passing through the center of the wafer W / reference work SW, the correction image may be inverted with respect to the line of symmetry before being used for correction.

[0088] Furthermore, the scanning methods shown in the protective film inspection apparatuses of the first to fourth embodiments are merely examples, and may be appropriately selected from the following. (1) The entire surface of the protective film p is scanned by combining linear movement along the X-axis direction and angle adjustment around the θ-axis. (2) The entire surface of the protective film p is scanned by combining linear motion along the X-axis direction and linear motion along the Y-axis direction.

[0089] Furthermore, the protective film inspection apparatus of the second to fourth embodiments has the apparatus configuration exemplified in FIG. 1, but is not limited to this apparatus configuration, and may have, for example, an apparatus configuration shown in FIG. In this modified example, the irradiation unit 10 and detection unit 30 shown in FIG. 1 are fixedly arranged in a common measurement unit U, and the measurement unit U is moved linearly along the X-axis direction in combination with the wafer W being rotated around the vertical axis by the θ-axis angle adjustment unit 43, thereby enabling irradiation of ultraviolet light onto the protective film p and reception of fluorescent light. The optical axis of the irradiation unit 10 and the optical axis of the detection unit 30 are perpendicular to each other, and a dichroic mirror dm is disposed at an angle at their intersection. That is, the dichroic mirror dm has an inclination angle of 45° with respect to the optical axis of the irradiation unit 10, and similarly, the dichroic mirror dm also has an inclination angle of 45° with respect to the optical axis of the detection unit 30. Furthermore, the measurement unit U is configured to be able to advance and retreat along the X-axis direction by an X-axis direction position adjustment unit 42.

[0090] According to the modified example of the above configuration, ultraviolet light is irradiated from the irradiation unit 10 toward the dichroic mirror dm upon receiving instructions from the control unit 50. This ultraviolet light is reflected by the dichroic mirror dm, bent 90 degrees, and irradiated onto the protective film p of the wafer W directly below. The protective film p emits fluorescence in response to the ultraviolet light. The portion of this fluorescence that passes through the dichroic mirror dm directly upward is received by the detector 31 of the detection unit 30, and its fluorescence intensity is measured. By simultaneously measuring the fluorescence intensity in this manner while the X-axis position adjustment unit 42 linearly moves the measurement unit U along the X-axis direction and the θ-axis angle adjustment unit 43 rotates the wafer W, the entire surface of the protective film p can be scanned. This allows the protective film inspection methods described in the second to fourth embodiments to be implemented in a similar manner. [Explanation of symbols]

[0091] 10 Irradiation unit 30 Detection unit (measurement unit) 50 control section p Protective film S1 Fading process S2 measurement process S1A, S1B Protective film application process to reference workpiece (preparation process) S2A,S2B 1st measurement process (preparation process) S3B Threshold distribution calculation process S3, S5A, S5B inspection process S3A 2nd measurement process (main measurement process) S4A Image correction process (correction process) SW reference work va Field of view (measurement field range) W Wafer (workpiece)

Claims

1. A method for inspecting the coating state of a protective film containing a light absorbing agent coated on a workpiece, comprising: a measuring step of measuring the fluorescence intensity of the fluorescence emitted by the light-absorbing agent when irradiated with excitation light; an inspection step of inspecting the coating state of the protective film based on the fluorescence intensity data obtained in the measurement step; a bleaching step, which is performed before the measurement step, by irradiating the protective film with the excitation light to bleach the light absorbent; A protective film inspection method comprising:

2. A method for inspecting the coating state of a protective film containing a light absorbing agent coated on a workpiece, comprising: a main measurement step of irradiating the protective film with excitation light having a wavelength absorbed by the light-absorbing agent, and measuring the fluorescence intensity of the light-absorbing agent emitting light in response to the irradiation of the excitation light, thereby obtaining uncorrected fluorescence intensity data; a preparatory step of measuring the fluorescence intensity of the fluorescence emitted by the light absorbent of the protective film applied to the reference workpiece to obtain correction data under the same fading conditions of the fluorescence intensity, including the application conditions of the protective film and the irradiation conditions of the excitation light, as those of the main measurement step; a correction step of correcting the uncorrected fluorescence intensity data obtained in the main measurement step based on the correction data obtained in the preparation step to obtain corrected fluorescence intensity data; an inspection step of inspecting the coating state of the protective film using the corrected fluorescent intensity data; A protective film inspection method comprising:

3. In the correction step, The corrected fluorescence intensity data is A, the corrected data is B, the uncorrected fluorescence intensity data is C, and arbitrary constants a and b, both of which are greater than 0, are used to obtain the corrected fluorescence intensity data A for each location along the surface of the workpiece using the following formula 1 or formula 2:

3. The protective film inspection method according to claim 2. [Equation 1]

4. A method for inspecting the coating state of a protective film containing a light absorbing agent coated on a workpiece, comprising: a main measurement step of irradiating the protective film with excitation light having a wavelength absorbed by the light-absorbing agent and measuring the fluorescence intensity of the light-absorbing agent that emits light in response to the irradiation of the excitation light; a preparatory step of measuring the fluorescence intensity of the fluorescence emitted by the light absorbent of the protective film applied to the reference workpiece to obtain correction data under the same fading conditions of the fluorescence intensity, including the application conditions of the protective film and the irradiation conditions of the excitation light, as those of the main measurement step; a threshold distribution calculation step of calculating a threshold distribution along the surface of the workpiece based on the correction data obtained in the preparation step; an inspection step of inspecting the coating state of the protective film by comparing the fluorescence intensity obtained in the main measurement step with the threshold distribution obtained in the threshold distribution calculation step; A protective film inspection method comprising:

5. In the threshold distribution calculation step, The threshold distribution is obtained by obtaining the corrected threshold A1 for each location along the surface of the workpiece using the following (Equation 3), where A1 is the corrected threshold, B1 is the correction data, and a1 is an arbitrary constant greater than 0.

5. The protective film inspection method according to claim 4. A1=a1*B1...(Formula 3)

6. As the reference workpiece, another workpiece on which a device having the same pattern as the workpiece to be measured in the main measurement process is mounted is used.

6. The protective film inspection method according to claim 2, wherein the protective film inspection method comprises:

7. An apparatus for inspecting the coating state of a protective film containing a light absorbing agent that is applied to a workpiece, comprising: an irradiation unit that irradiates the protective film with excitation light having a wavelength that is absorbed by the light absorbent; a measurement unit that measures the fluorescence intensity of the light-absorbing agent that emits light when irradiated with the excitation light; a control unit that controls the irradiation unit and the measurement unit; Equipped with The control unit The protective film is irradiated with the excitation light from the irradiation unit before measurement by the measurement unit, thereby bleaching the fluorescence emitted by the light absorbent. A protective film inspection device characterized by:

8. An apparatus for inspecting the coating state of a protective film containing a light absorbing agent that is applied to a workpiece, comprising: an irradiation unit that irradiates the protective film with excitation light having a wavelength that is absorbed by the light absorbent; a measurement unit that measures the fluorescence intensity of the light-absorbing agent that emits light upon being irradiated with the excitation light, and obtains uncorrected fluorescence intensity data; a control unit that controls the irradiation unit and the measurement unit and corrects the pre-correction fluorescence intensity data taking into account fading of the fluorescence emitted by the light absorbent; Equipped with The control unit Separately from the main measurement in which the workpiece is the measurement target, a reference workpiece is used instead of the workpiece, and the fading conditions for the fluorescence intensity, including the application conditions of the protective film and the irradiation conditions of the excitation light, are set to be the same as those for the main measurement, and then the fluorescence intensity of the fluorescence emitted by the light absorbent of the protective film applied to the reference workpiece is measured to obtain correction data; The uncorrected fluorescence intensity data obtained in the main measurement is corrected based on the correction data. A protective film inspection device characterized by:

9. An apparatus for inspecting the coating state of a protective film containing a light absorbing agent that is applied to a workpiece, comprising: an irradiation unit that irradiates the protective film with excitation light having a wavelength that is absorbed by the light absorbent; a measuring unit that measures the fluorescence intensity of the light-absorbing agent that emits light upon being irradiated with the excitation light to obtain fluorescence intensity data; a control unit that controls the irradiation unit and the measurement unit, sets a threshold distribution that takes into account fading of the fluorescence emitted by the light absorbent, and inspects the coating state of the protective film; Equipped with The control unit Separately from the main measurement in which the workpiece is the measurement target, a reference workpiece is used instead of the workpiece, and the fading conditions for the fluorescence intensity, including the application conditions of the protective film and the irradiation conditions of the excitation light, are set to be the same as those for the main measurement, and then the fluorescence intensity of the fluorescence emitted by the light absorbent of the protective film applied to the reference workpiece is measured to obtain correction data; setting the threshold distribution along the surface of the workpiece based on the correction data; The protective film is inspected by comparing the fluorescence intensity data obtained in the main measurement with the threshold distribution. A protective film inspection device characterized by:

10. The irradiation range of the excitation light and the measurement field of view range of the excitation light are moved spirally or concentrically on the workpiece while being overlapped with each other on the workpiece, The control unit controls the relative positions of the workpiece, the irradiation unit, and the measurement unit.

10. The protective film inspection device according to claim 7, wherein:

11. The irradiation range of the excitation light and the measurement field of view range of the excitation light are moved linearly on the workpiece while being overlapped with each other on the workpiece, The control unit controls the relative positions of the workpiece, the irradiation unit, and the measurement unit.

10. The protective film inspection device according to claim 7, wherein:

12. The measurement unit includes one of a photomultiplier tube, a line sensor camera, an area sensor camera, and a spectrometer.

10. The protective film inspection device according to claim 7, wherein:

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