Method for automatically inspecting, classifying and removing wafer defect

Abstract

Provided is a method for automatically inspecting, classifying, and removing a wafer defect, the method comprising: a first step of inspecting a defect by photographing the surface of a wafer with a camera unit; a second step of determining whether the defect can be removed and any one of a plurality of removal methods for the defect in accordance with a preset criterion, thereby automatically classifying the defect; a third step of moving a defect removal module to a target position where the defect is located if the defect is a removable type; a fourth step of removing the defect by selecting any one unit in the defect removal module in accordance with the removal method for the defect; and a fifth step of checking whether the defect is removed.

Description

Method for automatically inspecting, classifying, and removing defects in wafers

[0001] The present invention relates in particular to a method for automatically performing the entire process of inspecting a wafer, determining various defects on the wafer, classifying them accordingly, and ultimately removing them.

[0002] Optical inspection equipment is typically used to inspect for defects in substrates such as semiconductor wafers. Conventionally, optical inspection of semiconductor wafers was conducted by comparing black-and-white images captured by a mono camera. However, this method struggled to accurately identify various types of defects, making automatic defect classification difficult and reducing inspection reliability.

[0003] Additionally, if a defect is discovered on the wafer, it can be removed using a cleaning device. However, this process relies on manual intervention by the operator, or, if not, results in the wafer being discarded altogether, resulting in problems such as reduced product yield and loss of manufacturing costs.

[0004] In addition, there were problems such as the operator's inevitability in the overall process, from inspection of wafers to classification and removal of defects based on the results, and differences in productivity and labor consumption depending on the operator's skill level.

[0005] An embodiment of the present invention has been devised to solve the above problems, and provides a method for automatically inspecting defects on a wafer, automatically classifying them, and automatically removing them.

[0006] We aim to improve the reliability of wafer inspection results through an algorithm that minimizes misjudgments during the inspection stage. During the classification stage, we aim to ensure that defects are accurately classified according to pre-defined criteria. In the removal stage, we aim to provide a module that allows for selecting different methods depending on the type of defect on the wafer.

[0007] The purpose is to provide a module that prevents floating substances generated during the process of removing defects from remaining on the wafer.

[0008] An embodiment of the present invention provides a method for automatically inspecting, classifying, and removing defects in a wafer, comprising: a first step of inspecting a defect by capturing an image of the surface of a wafer with a camera unit; a second step of automatically classifying the defect by determining whether the defect is removable and which of a plurality of removal methods for the defect is used according to preset criteria; a third step of moving a defect removal module to a target position where the defect is located if the defect is a removable type; a fourth step of removing the defect by selecting a unit in the defect removal module according to the removal method for the defect; and a fifth step of confirming whether the defect is removed.

[0009] It is preferable that the above first step inspects for the defect by comparing 1) a reference image obtained by preprocessing an original image of the surface of the wafer and 2) a comparison image obtained by applying a color filter to a color scanned image of the surface of the wafer to minimize the difference in brightness.

[0010] In the second step, the removal method is preferably one of a first removal method of spraying gas toward the target location and its surroundings, a second removal method of irradiating a laser beam to the target location, and a third removal method of using the gas and the laser beam simultaneously, depending on the type of the defect.

[0011] In the third step, it is preferable that the defect removal module includes a cleaning unit that detaches the defect in a process of rapidly shrinking and then rapidly expanding the defect (foreign substance) through physical collision of the gas with the defect in response to the first removal method.

[0012] The third removal method preferably removes the defect by spraying the gas to cool the wafer and irradiating the laser beam.

[0013] Between the fourth and fifth steps, it is preferable to further include a fourth step for sucking up floating matter generated in the process of removing the defect.

[0014] The above floating material is sucked by a suction unit, and it is preferable that a suction part having a circular cross-section is formed on one side of the suction unit so that the floating material is sucked in a radial direction and is recessed inward.

[0015] According to the problem-solving means of the present invention as discussed above, various effects, including the following, can be expected. However, the present invention is not established only if it exhibits all of the following effects.

[0016] A method according to one embodiment of the present invention enables automatic inspection of defects on a wafer, automatic classification thereof, and automatic removal thereof.

[0017] Furthermore, this method can improve the reliability of wafer inspection results through an algorithm that minimizes misjudgments during the inspection stage. Furthermore, this method can accurately classify defects according to pre-established criteria during the classification stage. Furthermore, this method can select different methods during the removal stage depending on the type of defect on the wafer. Furthermore, this method can prevent floating particles and other debris generated during the defect removal process from remaining on the wafer.

[0018] FIG. 1 is a flowchart of a method for automatically inspecting, classifying, and removing defects in a wafer according to one embodiment of the present invention.

[0019] Figure 2 is a drawing roughly showing the process of creating a comparison target image with minimized difference in brightness in Figure 1.

[0020] Figure 3 is a schematic diagram of a defect removal module according to one embodiment of the present invention.

[0021] Figure 4 is a schematic diagram showing an enlarged portion of the lower part of Figure 3.

[0022] Figure 5 is a schematic diagram showing the operation method of the laser unit of Figure 3.

[0023] Figure 6 is a schematic diagram showing the operation method of the cleaning unit of Figure 3.

[0024] Figure 7 is a schematic diagram of Figure 4 viewed from above.

[0025] To fully understand the structure and effects of the present disclosure, preferred embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below, and can be implemented in various forms and subject to various modifications. In the following description of the present invention, detailed descriptions of related known functions that are obvious to those skilled in the art and that may unnecessarily obscure the gist of the present invention will be omitted.

[0026] While terms like "first" and "second" may be used to describe various components, these components should not be limited by these terms. These terms may only be used to distinguish one component from another. For example, without departing from the scope of the present disclosure, a first component could be referred to as a "second component," and similarly, a second component could also be referred to as a "first component."

[0027] In this application, terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but should be understood not to exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0028] The terminology used in this application is solely for the purpose of describing specific embodiments and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. Unless otherwise defined, terms used in the embodiments of this disclosure are to be interpreted as having the meanings commonly known to those skilled in the art.

[0029] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.

[0030] FIG. 1 is a flowchart illustrating a method for automatically inspecting, classifying, and removing defects in a wafer according to one embodiment of the present invention. Referring to FIG. 1, the method for automatically inspecting, classifying, and removing defects in a wafer (W) according to one embodiment of the present invention may include steps 1 (S10) to 5 (S50). Here, steps 1 to 5 may be performed automatically.

[0031] The first step is a step of inspecting the surface of a wafer (W) for defects by capturing an image with a camera unit (100). (S10) In one embodiment, the wafer (W) is merely an example of one of the inspection targets, and if the actual use is as an inspection substrate, the material such as glass or metal is irrelevant. Before the first step, the wafer (W) may be preceded by processes such as loading and alignment.

[0032] Fig. 2 is a drawing roughly showing the process of creating a comparison target image with minimized difference in brightness of Fig. 1. Referring to Fig. 2, more specifically, the first step can inspect for defects by comparing 1) a reference image obtained by preprocessing an original image of the surface of a wafer (W) and 2) a comparison target image (CI) with minimized difference in brightness by applying a color filter to a scanned image (SI) obtained by color scanning the surface of a wafer (W).

[0033] Here, the original image refers to a color image captured using a normal wafer (W). Furthermore, preprocessing may be performed on a portion or all of at least one randomly selected original image. Furthermore, image preprocessing may be the same process as converting a scanned image (SI) into a comparison target image (CI).

[0034] And, the scan image (SI) refers to a color image that is captured with respect to the wafer (W) that is the inspection target, i.e., that includes a defect. The color filter may include, for example, an R (red) filter, a G (green) filter, a B (blue) filter, an H (hue) filter, an S (saturation) filter, and a V (value) filter. The scan image (SI) may be first converted into a filter image (FI) to which the R filter, the G filter, the B filter, the H filter, the S filter, and the V filter are respectively applied. At this time, the filter image (FI) is a black and white image. Then, the filter image (FI) may be secondarily converted into a smoothed image with visually improved brightness by a preset histogram equalization algorithm. Then, the comparison target image (CI) may be generated by combining any one or at least one of a total of six smoothed images by a preset algorithm.

[0035] That is, the first step is to automatically detect defects on the wafer (W), which is the inspection target, by generating a black and white image with no or minimal difference in brightness from a color image generated through a camera unit (100) and then comparing them with each other.

[0036] The second step is to automatically classify defects by determining whether the defect can be removed and which of multiple removal methods can be used for the defect, based on preset criteria. (S20)

[0037] Referring to [Table 1] below, defects can be classified into multiple types. Defects include bumps (B), foreign substances (C), and discoloration on the surface of the wafer (W). Foreign substances (C) include metallic and organic substances. At this time, defects can be automatically classified into one of multiple types based on preset criteria. Furthermore, whether classified defects can be removed can be automatically determined based on preset criteria. Furthermore, a removal method for classified defects can be automatically determined based on preset criteria.

[0038]

[0039] Defect Type Removal Possible Removal MethodMissing Pattern (Bump) Impossible - Scratch Impossible - Foreign Material Possible Third Removal MethodPR Residue Possible Second Removal MethodUnformed Pattern (Bump) Impossible - Pattern (Bump) dent Impossible - Lump / Nodule Impossible - Bump Discoloration Possible Third Removal MethodRaw Material Possible First Removal MethodMetal Corrosion Possible Second Removal MethodPitting Impossible - Pattern (Bump) Misalign Impossible - Big Pattern (Bump) Impossible - Bridged Pattern (Bump) (Short) Impossible - Missing Pattern (Bump) Impossible - Passivation Damage Possible First Removal MethodUBM Residue Possible First Removal MethodScratch Impossible - Parasitic Bump Possible First Removal MethodForeign Material Possible Third Removal MethodSmall Bump Impossible - Unformed Bump Impossible - Pattern (Ball) Abnormal Impossible - Passivation Discoloration Possible 1st Removal Method RDL Discoloration Possible 1st Removal Method PSV Wrinkle Possible 1st Removal Method RDL Open Impossible - Pattern (Bump) Discoloration Impossible 1st Removal Method

[0040] In one embodiment, whether or not removal is possible can be classified into, for example, possible and impossible. In addition, the removal method can be classified into, for example, one of a first removal method to a third removal method depending on the type of defect. First, the first removal method is a method of removing a defect by spraying gas toward a target location and its surrounding area. Then, the second removal method is a method of removing a defect by irradiating a laser beam (L) to the target location. In addition, the third removal method is a method of removing a defect using gas and a laser beam (L) simultaneously. Here, the target location refers to the location of a defect existing on the surface of the wafer (W).

[0041] Meanwhile, if it is impossible to remove a defect, the defect may be removed through a manual removal process by an operator, etc., rather than through an automatic removal process by a preset algorithm or without going through a removal step.

[0042] FIG. 3 is a schematic diagram of a defect removal module according to one embodiment of the present invention, FIG. 4 is an enlarged schematic diagram of a lower portion of FIG. 3, FIG. 5 is a schematic diagram showing the operation method of the laser unit of FIG. 3, and FIG. 6 is a schematic diagram showing the operation method of the cleaning unit of FIG. 3.

[0043] The third step is a step of moving the defect removal module to the target position where the defect is located if the defect is of a removable type. (S30) Here, the defect removal module constitutes a part of the cleaner device. The defect removal module can be moved to the target position by, for example, a moving unit (not shown). The moving unit can move the defect removal module to the corresponding coordinates by address data including the coordinates of the target position, etc. In addition, the cleaner device according to one embodiment may include the camera unit (100) described above.

[0044] Meanwhile, the defect removal module may include a cleaning unit (400), a laser unit (200), a suction unit (500), etc. The cleaning unit (400) rapidly shrinks the defect (including foreign substances) through physical collision of gas with the defect (including foreign substances) in response to the first removal method, and then rapidly expands the defect, thereby detaching the defect (including foreign substances).

[0045] The cleaning unit (400) may include a spray nozzle (410) capable of spraying gas. In one embodiment, the cleaning unit may spray gas toward a target location and its surroundings. Here, the gas may be a cooling gas. In one embodiment, the cooling gas is sprayed at high pressure and may include solid CO2 pellets. In addition, the CO2 pellets (P) are preferably solid carbon dioxide (dry ice) formed in a size of several to several tens of micrometers.

[0046] At this time, the process of detaching the defect (foreign substance) will be described in detail. The CO2 pellet (P) having a temperature in the range of -70 to -80 degrees Celsius collides with the defect (foreign substance) and freezes the defect (foreign substance). In the process, the defect (foreign substance) rapidly contracts due to the temperature difference with the surroundings, causing a crack to occur. At this time, the CO2 pellet (P) injected at high speed may partially enter the cracks of the defect (foreign substance) or the gap between the defect (foreign substance) and the wafer (W). In addition, the CO2 pellet (P) that enters the defect (foreign substance) may sublimate and its volume may expand by more than 800 times in one embodiment.

[0047] Meanwhile, since the CO2 pellets (P) sublimate into gas at room temperature, secondary contamination by the cooling gas itself can be prevented. As the CO2 pellets (P) expand, defects (foreign substances) may be broken by the expansion force or separated from the surface of the wafer (W). The cleaning unit (400) can repeat this process to remove defects (foreign substances) attached to the surface of the wafer (W). Meanwhile, floating substances may be generated during the defect (foreign substance) removal process by the cleaning unit (400).

[0048] The laser unit (200) irradiates a laser beam (L) to a target position to which a defect (including foreign substances) is attached in response to the second removal method, thereby removing the defect (including foreign substances). The laser unit (200) generates a laser beam (L) having a preset wavelength, pulse width, and output conditions. The laser unit (200) can generate a single pulse or multiple pulse laser beam (L). In addition, the laser beam (L) can be appropriately selected depending on the defect. In addition, the laser scanner unit (210) can adjust the optical axis of the laser beam (L) so that the laser beam (L) is irradiated to a preset position. Meanwhile, floating objects may be generated in the process of removing a defect (foreign substance) using the laser beam (L).

[0049] The third removal method is a method of removing defects by spraying gas to cool the wafer (W) and irradiating it with a laser beam (L). This method uses a cleaning unit (400) and a laser unit (200) together.

[0050] According to one embodiment of the present invention, in a defect (foreign matter) removal processing process by a laser unit (200), the cleaning unit (400) may be set to spray solid carbon dioxide to prevent thermal damage to the wafer (W), thereby simultaneously cooling the wafer (W) and blowing away floating matter generated during the defect (foreign matter) removal process.

[0051] That is, the cleaning unit (400) can be operated simultaneously during the defect (foreign substance) removal process by the laser unit (200). In one embodiment, the aforementioned CO2 pellet (P) has been confirmed to be suitable as a cooling gas and a blowing gas through our internal experiments.

[0052] Step 4 is a step of removing a defect by selecting a unit within the defect removal module according to a removal method for the defect. (S40) In one embodiment, any unit may be selected corresponding to the first removal method to the third removal method. In the case of the first removal method, the cleaning unit (400) may be selected, in the case of the second removal method, the laser unit (200) may be selected, and in the case of the third removal method, the cleaning unit (400) and the laser unit (200) may be selected.

[0053] Step 5 is a step for determining whether a defect has been removed (S50). This step may be performed, for example, only on defects determined to be removable. Step 5 may be performed automatically via a camera unit (100).

[0054] Meanwhile, between the fourth and fifth steps, a fourth-first step for sucking floating matter generated during the process of removing defects (foreign substances) may be further included. In one embodiment, the suction unit (500) may suck floating matter generated by the laser unit (200) and / or the cleaning unit (400). At this time, the suction unit (500) operates simultaneously with the laser unit (200) and / or the cleaning unit (400) to prevent floating matter from reattaching to the surface of the wafer (W). At this time, the suction unit (500) may be arranged between the objective lens unit (300) and the wafer (W). Meanwhile, the suction unit (500) may include a suction unit (510) for sucking air at the target position and its surrounding area. In one embodiment, the suction unit (510) may be formed on one side of the suction unit (500).

[0055] Fig. 7 is a schematic diagram of Fig. 4 viewed from above. Referring to Fig. 7, a suction portion (510) is recessed into the inside of the suction unit (500) and may have a circular cross-section so that floating objects are sucked in a radial direction. Such a suction portion (510) can improve suction performance by generating an isotropic flow for floating objects.

[0056] Meanwhile, the inner diameter of the suction part (510) refers to the inner diameter of a circle formed by the cross section of the suction part (510). In one embodiment, the target position may be located at the inner diameter of the suction part (510). That is, the center of the inner diameter of the suction part (510) may be arranged on the optical axis of the objective lens part (300) or may be arranged on the optical path of the objective lens part (300). Alternatively, the center of the inner diameter of the suction part (510) may be arranged on the optical path of the camera unit (100). According to one embodiment, the inner diameter (second diameter) of the suction part (510) is preferably equal to or larger than the outer diameter (first diameter) of the objective lens part (300).

[0057] Referring again to FIG. 7, the cleaning unit (400) may be arranged to face the suction unit (510) and configured to spray carbon dioxide in a dry ice state toward the suction unit (510) during operation of the suction unit (500). For example, the cleaning unit (400) may be arranged on one open side of the suction unit (510). At this time, the cleaning unit (400) may generate anisotropic air flow so that floating objects are guided toward the suction unit (510).

[0058] In addition, as described above, the cleaning unit (400) can cool the surface of the wafer (W) during the defect (foreign substance) removal process by the laser unit (200) by spraying cooling gas. For example, the cooling gas sprayed by the cleaning unit (400) can be reflected on the surface of the wafer (W) and guided toward the suction unit (510).

[0059] Although the preferred embodiments of the present invention have been described above by way of example, the scope of the present invention is not limited to these specific embodiments, and may be appropriately modified within the scope described in the claims.

Claims

1. The first step is to inspect the surface of the wafer for defects by capturing the image with a camera unit; A second step of automatically classifying the defect by determining whether the defect can be removed and which of a plurality of removal methods for the defect is used based on preset criteria; If the above defect is of a removable type, a third step of moving the defect removal module to the target location where the defect is located; A fourth step of removing the defect by selecting a unit within the defect removal module according to the removal method for the defect; and A method for automatically inspecting, classifying and removing defects in a wafer, comprising a fifth step of confirming whether the above defects have been removed.

2. In paragraph 1, The above first step is a method for automatically inspecting, classifying and removing defects in a wafer by comparing 1) a reference image obtained by preprocessing an original image of the surface of the wafer and 2) a comparison image in which the difference in brightness is minimized by applying a color filter to a scanned image of the surface of the wafer in color.

3. In the first paragraph, in the second step, The above removal method is a method for automatically inspecting, classifying and removing a defect in a wafer, wherein the above removal method is one of a first removal method of spraying gas toward the target position and its surrounding area, a second removal method of irradiating a laser beam to the target position, and a third removal method of using the gas and the laser beam simultaneously, depending on the type of the defect.

4. In the third paragraph, in the third step, A method for automatically inspecting, classifying and removing defects in a wafer, the above defect removal module including a cleaning unit that rapidly shrinks and then rapidly expands the defect (foreign matter) through physical collision of the gas with the defect (foreign matter) in response to the first removal method.

5. In paragraph 3, The third removal method is a method for automatically inspecting, classifying and removing defects in a wafer by spraying the gas to cool the wafer and irradiating the laser beam to remove the defects.

6. In paragraph 1, Between the above 4th step and the above 5th step, A method for automatically inspecting, classifying and removing defects in a wafer, further comprising a step 4-1 of sucking up floating matter generated in the process of removing the above defects.

7. In paragraph 6, The above floating material is sucked by the suction unit, A method for automatically inspecting, classifying and removing defects in a wafer, wherein a suction unit having a circular cross-section is formed on one side of the above suction unit so that floating matter is sucked in a radial direction.

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