JP2011174764A - Inspecting method and inspecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspecting method capable of readily inspecting a film of a surface of a wafer with high sensitivity. <P>SOLUTION: The inspecting method employs an inspecting device that includes: a stage for supporting a wafer having a film provided on its surface; a lighting system for projecting illumination light to the surface of the wafer supported by the stage; a detector for detecting reflection light from the surface of the wafer to which the illumination is projected; and an inspection unit for inspecting the film, based on information about the reflection light detected by the detector. The inspecting method includes a setting step S101 of setting a target film thickness and a refraction index, a computation step S102 of computing a characteristic of change in the refraction index with respect to change in the film thickness in the vicinity of the target film thickness in accordance with the target film thickness and the refraction index by each of a plurality of wavelengths, and a determination step S103 of determining that a wavelength in which the change in the refraction index (i.e., sensitivity) becomes maximum is made to be the wavelength of the illumination light on the basis of the characteristic of the change in the refraction index with respect to change in the film thickness. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an inspection method and an inspection apparatus for inspecting a state of a film on a substrate surface, particularly a state of a thin film on a wafer surface.

  As a semiconductor device is miniaturized, a process margin in manufacturing a semiconductor device is reduced. As a result, it is required to inspect the state of a thin film such as a resist film on the wafer surface more accurately on the entire wafer surface. Furthermore, the resist film tends to be thinner in order to increase the resolving power of an exposure apparatus that exposes a pattern on the wafer surface due to further miniaturization, and inspection with higher sensitivity is required.

  On the other hand, an apparatus is known that irradiates the wafer surface with illumination light, collects reflected light from the entire wafer surface as an image, and inspects the state of the film on the wafer surface based on the brightness of the image ( For example, see Patent Document 1). In such an apparatus, the brightness of an image changes due to a change in film thickness, and a portion with an abnormal brightness can be detected as a defect.

JP 2002-139451 A

  However, in such an apparatus, the sensitivity of the inspection may differ depending on the inspection conditions such as the film thickness, and a measure for performing a highly sensitive inspection by an easy method has been demanded.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an inspection method and an inspection apparatus capable of easily inspecting a film on a substrate surface with high sensitivity.

  In order to achieve such an object, an inspection method according to the present invention includes a stage that supports a substrate having a film provided on a surface thereof, an irradiation unit that irradiates illumination light onto the surface of the substrate supported by the stage, and A detection unit for detecting reflected light from the surface of the substrate irradiated with the illumination light; an inspection unit for inspecting the film from information on the reflected light detected by the detection unit; and a plurality of preset units An inspection method comprising a wavelength selection unit that selects the wavelength of the illumination light from the wavelengths of the light, a setting step of setting a target film thickness and a refractive index of the film, and the set target of the film Based on the calculated change characteristics, the calculation step of calculating a change characteristic of the reflected light with respect to the change of the film thickness in the vicinity of the target film thickness from the film thickness and the refractive index, and the wavelength based on the calculated change characteristics Selection And a determining step of determining a wavelength of the illumination light selectively in parts.

  In the inspection method described above, in the calculation step, the intensity change rate of the reflected light with respect to the change in the film thickness in the vicinity of the target film thickness is calculated from the set target film thickness and refractive index of the film. Preferably, the wavelength is calculated for each wavelength, and in the determining step, the wavelength at which the intensity change rate of the reflected light is maximized is determined as the wavelength of the illumination light selected by the wavelength selection unit.

  In the inspection method described above, in the calculation step, the intensity change of the reflected light with respect to the change in the film thickness in the vicinity of the target film thickness is determined from the set target film thickness and refractive index of the film in the plurality of wavelengths. It may be calculated every time, and in the determination step, the wavelength at which the intensity change of the reflected light becomes the most linear change may be determined as the wavelength of the illumination light selected by the wavelength selection unit.

  Further, the inspection method according to the present invention includes a stage that supports a substrate having a film provided on a surface thereof, an irradiation unit that irradiates illumination light onto the surface of the substrate supported by the stage, and the illumination light. A detection unit that detects reflected light from the surface of the substrate, an inspection unit that inspects the film by measuring the thickness of the film from information of the reflected light detected by the detection unit, and a preset setting. And a wavelength selection unit that selects a wavelength of the illumination light from a plurality of wavelengths, the target film thickness of the film, the complex refractive index of the film, and the complex refraction of the substrate A setting step of setting a rate, and the set target film thickness of the film, the complex refractive index of the film, and the complex refractive index of the substrate, the reflected light with respect to the change of the film thickness in the vicinity of the target film thickness Change characteristics of the plurality of wavelengths A calculating step of calculating, based on said variation characteristic that the calculated, and a determination step of determining a wavelength of the illumination light selected by the wavelength selection unit.

  In the above inspection method, in the calculation step, the change in the film thickness in the vicinity of the target film thickness is determined from the set target film thickness of the film, the complex refractive index of the film, and the complex refractive index of the substrate. Calculating the intensity change rate of the reflected light for each of the plurality of wavelengths, and in the determining step, the wavelength selecting unit selects a wavelength at which the intensity change rate of the reflected light is the largest as the wavelength of the illumination light It is preferable to determine.

  In the inspection method described above, in the calculation step, the change in the film thickness in the vicinity of the target film thickness from the set target film thickness of the film, the complex refractive index of the film, and the complex refractive index of the substrate. The intensity change of the reflected light with respect to is calculated for each of the plurality of wavelengths, and in the determining step, the wavelength selection unit selects a wavelength at which the intensity change of the reflected light is the most linear change. The wavelength may be determined.

  In the inspection method described above, the irradiation step of irradiating the surface of the substrate with illumination light using the illumination unit, and the reflected light from the surface of the substrate irradiated with the illumination light using the detection unit A detection step of detecting, and an inspection step of inspecting the film from information of the reflected light detected in the detection step using the inspection unit, and the change calculated in the calculation step in the inspection step Preferably, the film is inspected by determining the increase or decrease in the film thickness from the intensity of the reflected light detected in the detection step using characteristics.

  In the inspection method described above, the irradiation step of irradiating the surface of the substrate with illumination light using the illumination unit, and the reflected light from the surface of the substrate irradiated with the illumination light using the detection unit A detection step for detecting, and an inspection step for inspecting the film by measuring a film thickness of the film from information of the reflected light detected in the detection step using the inspection unit, The film thickness is calculated from the intensity of the reflected light detected in the detection step using the change characteristic calculated in the calculation step, and the film is inspected based on the calculated film thickness. May be.

  The inspection apparatus according to the present invention includes a stage that supports a substrate having a film provided on a surface thereof, an irradiation unit that irradiates illumination light on the surface of the substrate supported by the stage, and the illumination light. A detection unit for detecting reflected light from the surface of the substrate, an inspection unit for inspecting the film from information on the reflected light detected by the detection unit, and the illumination light from a plurality of preset wavelengths. A wavelength selection unit that selects a wavelength of the film, and the wavelength selection unit includes an input unit to which a target film thickness and a refractive index of the film are input, and a target film thickness and a refraction of the film that are input to the input unit. From the ratio, a calculation unit that calculates a change characteristic of the reflected light with respect to a change in the film thickness in the vicinity of the target film thickness for each of the plurality of wavelengths, and the wavelength based on the change characteristic calculated by the calculation unit The reference to be selected by the selection unit And a determining section for determining the wavelength of light.

  The inspection apparatus according to the present invention includes a stage that supports a substrate having a film provided on a surface thereof, an irradiation unit that irradiates illumination light on the surface of the substrate supported by the stage, and the illumination light. A detection unit that detects reflected light from the surface of the substrate, an inspection unit that inspects the film by measuring the thickness of the film from information of the reflected light detected by the detection unit, and a preset setting. A wavelength selection unit that selects a wavelength of the illumination light from a plurality of wavelengths, and the wavelength selection unit inputs a target film thickness of the film, a complex refractive index of the film, and a complex refractive index of the substrate And the reflection with respect to the change of the film thickness in the vicinity of the target film thickness from the target film thickness of the film input to the input unit, the complex refractive index of the film, and the complex refractive index of the substrate Calculates light change characteristics for each of the plurality of wavelengths. That a calculating unit, on the basis of the said variation characteristic calculated by the calculation unit, and a determination unit for determining a wavelength of the illumination light selected by the wavelength selection unit.

  According to the present invention, the film on the substrate surface can be easily inspected with high sensitivity.

It is a flowchart which shows the inspection method of this embodiment. It is a figure which shows the surface inspection apparatus of this embodiment. It is a graph which shows the relationship between a film thickness and a reflectance. It is a graph which shows the relationship between a film thickness and a reflectance about several wavelengths. It is a graph which shows the relationship between a film thickness and the 1st derivative of a reflectance about several wavelengths. It is a graph which shows the relationship between a film thickness, a reflectance, the primary derivative of a reflectance, and the secondary derivative of a reflectance.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The surface inspection apparatus of this embodiment is shown in FIG. 2, and the surface of a semiconductor wafer W (hereinafter referred to as wafer W), which is a substrate to be tested, is inspected by this apparatus. The surface inspection apparatus 1 according to the present embodiment includes a stage 10 that supports a wafer W formed in a substantially disk shape, and the wafer W transferred by a transfer apparatus (not shown) is placed on the stage 10. At the same time, it is fixed and held by vacuum suction. A film such as a resist film is provided on the surface of the wafer W. The stage 10 supports the wafer W so that the wafer W can be rotated (rotated within the surface of the wafer W) about the rotational symmetry axis of the wafer W (the central axis of the stage 10). The stage 10 can tilt (tilt) the wafer W around an axis passing through the surface of the wafer W, and can adjust the incident angle of illumination light.

  The surface inspection apparatus 1 further includes an illumination system 20 that irradiates the surface of the wafer W supported by the stage 10 with illumination light, and a light receiving system 30 that collects light from the wafer W when irradiated with illumination light. The imaging apparatus 35 that receives the light condensed by the light receiving system 30 and captures an image of the surface of the wafer W, an image processing unit 40, a wavelength selection unit 45, and a control unit 50 are configured. The illumination system 20 includes an illumination unit 21 that emits illumination light, and an illumination-side elliptic mirror 25 that reflects the illumination light emitted from the illumination unit 21 toward the surface of the wafer W. The illumination unit 21 includes a light source unit 22 such as a metal halide lamp or a mercury lamp, a light control unit 23 that extracts light having a predetermined wavelength from the light from the light source unit 22 and adjusts the intensity, and a light control unit 23 The light guide fiber 24 is configured to guide light to the illumination-side elliptical mirror 25 as illumination light.

  The dimming unit 23 includes a plurality of wavelength selection filters (not shown), and the illumination light is selected by inserting any one of the plurality of wavelength selection filters into the optical path. For example, the wavelength of 313 nm, 365 nm, 405 nm, 436 nm, and 546 nm can be selected. Then, the light from the light source unit 22 passes through the dimming unit 23, and illumination light having a predetermined wavelength is emitted from the light guide fiber 24 to the illumination side elliptical mirror 25, and from the light guide fiber 24 to the illumination side elliptical mirror 25. The emitted illumination light is held on the stage 10 as parallel (telecentric) light by the illumination-side elliptical mirror 25 because the emission part of the light guide fiber 24 is disposed on the focal plane of the illumination-side elliptical mirror 25. The surface of the wafer W is irradiated. As a result, illumination is performed at the same angle condition at any location on the surface of the wafer W.

  Light emitted from the surface of the wafer W (for example, regular reflection light) is collected by the light receiving system 30. The light receiving system 30 is mainly configured by a light receiving side elliptical mirror 31 disposed to face the stage 10, and emitted light (for example, specularly reflected light) collected by the light receiving side elliptical mirror 31 is captured by the imaging device 35. The image of the wafer W (for example, a regular reflection image) is formed. The imaging device 35 photoelectrically converts the image of the surface of the wafer W formed on the imaging surface to generate an image signal, and outputs the image signal to the image processing unit 40. The light-receiving side elliptical mirror 31 is set so that the reflected light from any part of the surface of the wafer W can be detected under the same angle condition. Thus, by making both the illumination system 20 and the light receiving system 30 telecentric, images of the same angle condition can be obtained at all locations on the surface of the wafer W.

  The image processing unit 40 generates a digital image of the wafer W based on the image signal of the wafer W input from the imaging device 35. Further, the image processing unit 40 inspects the presence or absence of a defect (abnormality) on the surface of the wafer W based on the generated image (digital image) of the wafer W. Then, the inspection result by the image processing unit 40 and the image of the wafer W at that time are output and displayed by an image display device (not shown). Defects (abnormalities) detected by the image processing unit 40 are mainly film thickness non-uniformity of a film (resist film or the like) on the surface of the wafer W, and the non-uniform film thickness is image brightness due to light interference. Can be detected as a defect (abnormality) because it becomes brighter or darker than a normal part. For example, if there is a foreign substance when the resist film is applied, the non-uniform thickness part is formed in a comet shape (comet shape) with the part having the foreign substance as a head. Further, for example, when the resist discharge amount is insufficient when applying the resist film, it may be formed in a starfish shape near the outer periphery of the wafer W.

  The wavelength selection unit 45 is for selecting the wavelength of the illumination light from among a plurality of wavelengths (of the wavelength selection filter) set by the dimming unit 23 of the illumination unit 21, and data is input / output. An input / output unit 46 and a calculation unit 47 that performs various calculations for determining the wavelength of illumination light are configured. Further, the control unit 50 controls operations of the stage 10, the imaging device 35, the image processing unit 40, the wavelength selection unit 45, and the like.

  Here, a wavelength selection method by the wavelength selection unit 45 will be described. FIG. 3 is a graph showing the relationship between changes in film thickness and changes in reflectance. Here, the film thickness is a so-called geometric film thickness, but an optical film thickness (refractive index × geometric film thickness) may be used. The wafer W is obtained by applying a resist film on a silicon wafer (bare wafer), and the wavelength of illumination light is assumed to be 546 nm. Note that a method for calculating the reflectance of illumination light (on the surface of the wafer W) is disclosed in, for example, Japanese Patent Laid-Open No. 6-74716, and a detailed description thereof is omitted.

  In the graph shown in FIG. 3, when attention is paid to the film thickness of about 130 nm indicated as film thickness A, the reflectance change with respect to the film thickness change is close to a straight line and the slope of the graph is steepest in this vicinity. In the film thickness range of 130 ± 20 nm, the shape of the graph can be regarded as a substantially straight line. If the target film thickness of the resist film in the example of FIG. 3 is 130 nm and the variation range of the film thickness is ± 20 nm, the reflectance change changes linearly according to the film thickness change. The brightness of the image captured and acquired by 35, that is, the reflectance of the illumination light has a linear relationship with the film thickness. Therefore, it is possible to judge the quality by converting the brightness of the image into the film thickness, and conversely, the quality standard (for example, ± 10 nm) of the film thickness is converted into the judgment standard of the brightness fluctuation in the image. You can also.

  In general inspections, the target film thickness is determined in advance, so for all selectable wavelengths, the characteristics of reflectance change with respect to film thickness changes similar to those described above are examined, and the wavelength that is most advantageous for inspection is determined. Just choose. FIG. 4 is a graph showing the relationship between the change in the film thickness and the change in the reflectance for each of the wavelengths of the emission lines obtained from the mercury lamp, which are 313 nm, 365 nm, 405 nm, 436 nm, and 546 nm. In FIG. 4, conditions other than the illumination wavelength are the same as in FIG. Based on the calculation results of the characteristics shown in FIG. 4, if a wavelength having a large reflectance change is selected in the vicinity of the target film thickness of the wafer W to be inspected, an inspection with high sensitivity to the film thickness change can be performed. It becomes possible. In order to select a wavelength having a large reflectance change near the target film thickness, it is convenient to draw a curve obtained by first-order differentiation of the characteristics of the reflectance change (that is, the graph of FIG. 4). This is because, in order to select the wavelength at which the reflectance change with respect to the film thickness change is maximized, the wavelength at which the first-order differential coefficient is maximized in the vicinity of the target film thickness may be selected.

  Note that the location where the first-order differential coefficient is minimized is a location where the slope of the reflectance change is negative and the degree of reflectance change (absolute value) is maximized. Even in such a location, the change in film thickness can be detected with high sensitivity only by reversing the direction of the change in film thickness and the direction of the change in reflectivity. The wavelength that becomes may be selected as the wavelength of the illumination light. However, in the inspection of the wafer W, it is necessary to use it considering that the direction of the change in film thickness and the change in reflectance are opposite. That is, it is necessary to perform an inspection by determining whether the film thickness has increased or decreased from the brightness variation of the image (change in the intensity of reflected light).

  FIG. 5 is a graph showing the first derivative of the reflectance change of FIG. From FIG. 5, it can be seen that the peak height of the first-order differential coefficient differs depending on the wavelength of the illumination light, that is, the maximum value of the change rate of the reflectance change with respect to the film thickness change is different depending on the wavelength. Further, obtaining the most sensitive condition of the reflectance characteristic means obtaining a condition that maximizes the first derivative, and this can be obtained by obtaining the second derivative of the reflectance change in FIG. Find the condition that becomes zero. Thus, the optimum condition can be easily obtained by using the second derivative. FIG. 6 is a graph in which first and second derivative curves are added to the characteristic graph of FIG. It should be noted that appropriately displaying the graphs of FIGS. 3 to 6 and the like by an image display device or the like is useful for evaluating and confirming the validity of the selected wavelength.

  When using the wavelength thus selected and determined, since the relationship between the change in film thickness and the change in reflectance is known, a two-dimensional film thickness distribution can be obtained from a two-dimensional image having reflectance information. It is easy to convert to information simply. For example, it is assumed that the relationship between the change in film thickness near the target film thickness and the change in reflectance is expressed by the following equation (1).

  Here, R is a reflectance, T is a film thickness, and a and b are coefficients. The coefficient a can be obtained from the above-described first derivative (graph of FIG. 5). When the coefficient a is obtained, the coefficient b is derived from the relationship between the film thickness and the reflectance (graph of FIG. 3 or FIG. 4). (1) It can obtain | require using Formula. In order to convert the image information of the wafer W into the film thickness distribution information, the conversion using the equation (2) may be performed for each pixel in the image of the wafer W from the equation (1).

  An inspection method in which wavelength selection is performed as described above will be described with reference to the flowchart of FIG. First, the case where the purpose of the inspection is pass / fail judgment based on the film thickness value will be described. In this case, it is necessary to convert the image information of the wafer W imaged and acquired by the imaging device 35 into film thickness information. The characteristic of the reflectance change with respect to the film thickness change as shown in FIG. It is necessary to calculate accurately including This is because the coefficients a and b in the equations (1) and (2) cannot be obtained accurately unless the absolute value of the reflectance is accurate.

  Information necessary in this case includes the complex refractive index and target film thickness of the film on the surface of the wafer W, the complex refractive index of the base material (bare wafer) of the wafer W, and one or more other films between the film and the base material. If there is, there are a complex refractive index and a standard film thickness value of the other film. Therefore, first, information necessary for inspection (that is, complex refractive index of the film, target film thickness, etc.) is set (step S101). Specifically, information (such as a complex refractive index of the film and a target film thickness) necessary for inspection is input using an interface (not shown) such as a keyboard electrically connected to the control unit 50 or the like. At this time, information input from the interface is transmitted to the input / output unit 46 and the calculation unit 47 of the wavelength selection unit 45 via the control unit 50 and the like.

  Note that the complex refractive index of the film, the complex refractive index of the base material (bare wafer) of the wafer W, and the like are determined by at least one reference point (for example, wafer) by a refractive index measuring device using ellipsometry, for example. It can be specified by measuring the center position of W). Then, on the base material of the wafer W under the angle condition realized by the illumination by the illumination system 20 based on the complex refractive index for each wavelength specified in this way and the incident angle of the illumination light to the wafer W. When films having various thicknesses are formed, the reflectance including interference of reflected light from the front surface and the back surface of the film can be calculated.

  Accordingly, the calculation unit 47 changes the film thickness as shown in FIG. 4 (in the vicinity of the target film thickness) from the complex refractive index and target film thickness of the set film, the complex refractive index of the base material (bare wafer) of the wafer W, and the like. Is calculated for each of a plurality of wavelengths that can be selected by a wavelength selection filter (not shown) (step S102). At this time, a graph of the primary differential coefficient of the reflectance change as shown in FIG. 5 may be obtained, or a graph of the secondary differential coefficient of the reflectance change as shown in FIG. 6 may be obtained. Good.

  Next, the calculation unit 47 determines the wavelength of the illumination light selected by the wavelength selection unit 45 based on the calculated characteristic of the reflectance change with respect to the change in film thickness (step S103). At this time, the wavelength at which the reflectance change is maximized in the vicinity of the target film thickness is selected. At this time, as described above, the wavelength at which the primary differential coefficient of the reflectance change is maximized in the vicinity of the target film thickness may be selected, and the secondary differential coefficient of the reflectance change in the vicinity of the target film thickness is A wavelength that becomes zero may be selected. Note that when the wavelength of the illumination light is determined, the calculation unit 47 obtains the coefficients a and b of the equation (2) as described above.

  As described above, when the wavelength of the illumination light is selected by the wavelength selection unit 45, the wavelength selection signal is output from the wavelength selection unit 45 and input to the illumination unit 21 via the control unit 50. When the wavelength selection signal from the wavelength selection unit 45 is input to the illumination unit 21, the dimming unit 23 selects a wavelength selection filter (not shown) corresponding to the wavelength selected by the wavelength selection unit 45 on the optical path. Insert into. This enables inspection with high sensitivity to changes in film thickness. Note that the data of the coefficients a and b in the equation (2) obtained in the previous step is input to the image processing unit 40 via the control unit 50.

  When the wavelength of the illumination light is selected, the illumination light is irradiated onto the surface of the wafer W using the illumination system 20 (step S104). At this time, the light from the light source unit 22 passes through the light control unit 23, and illumination light having a wavelength selected by the wavelength selection unit 45 is emitted from the light guide fiber 24 to the illumination side elliptical mirror 25, and the light guide fiber 24. The illumination light emitted from the illumination side elliptical mirror 25 to the illumination side elliptical mirror 25 is applied to the surface of the wafer W held by the stage 10 as parallel (telecentric) light.

  When the illumination light is irradiated on the surface of the wafer W, the specularly reflected light reflected by the surface of the wafer W is collected by the light-receiving side elliptical mirror 31 and reaches the imaging surface of the imaging device 35, and an image of the wafer W ( A regular reflection image) is formed. Therefore, the imaging device 35 photoelectrically converts the image of the wafer W (by specular reflection light) formed on the imaging surface to generate an image signal, and outputs the image signal to the image processing unit 40 (step S105).

  The image processing unit 40 generates a digital image of the wafer W based on the image signal of the wafer W input from the imaging device 35, measures the film thickness from the generated image information of the wafer W, and forms a film on the surface of the wafer W. Is inspected (step S106). At this time, the image processing unit 40 calculates the reflectance R from the image information of the wafer W, and calculates the film thickness T from the calculated reflectance R using the above-described equation (2). The image processing unit 40 determines that the calculated film thickness T is normal if the calculated film thickness T is within the predetermined film thickness range, and determines that the calculated film thickness T is abnormal if the calculated film thickness T is outside the predetermined film thickness range. Further, the inspection result by the image processing unit 40 and the image of the wafer W at that time are output and displayed by an image display device (not shown). Note that the reflectance R and the film thickness T are calculated for each pixel in the image of the wafer W, and the film thickness distribution is measured over the entire surface of the wafer W and the film thickness non-uniformity is inspected. The reflectance R is the intensity of illumination light stored in advance in an internal memory (not shown) of the image processing unit 40 from the luminance value (signal intensity) in the image (pixel) of the wafer W, or the imaging device 35. And information such as the reflectance at the elliptical mirrors 25 and 31 are calculated.

  Next, a case where the inspection purpose is simple defect inspection will be described. In this case, it is only necessary to select a wavelength that enables inspection with the highest sensitivity. Therefore, in the characteristics of the reflectance change with respect to the film thickness change illustrated in FIG. 3, only the period and phase are important, and the absolute value of the reflectance may not be accurate.

  In this case, the minimum necessary information is the refractive index of the film on the surface of the wafer W (the real part of the complex refractive index) and the target film thickness. Therefore, first, as in the case of pass / fail judgment by the film thickness value, information necessary for performing the inspection (that is, the refractive index of the film and the target film thickness) is set (step S101). In the case of simple defect inspection, the refractive index of the film and the target film thickness are input using an interface (not shown) such as a keyboard.

  Next, the calculation unit 47 converts the reflectance change with respect to the film thickness change (in the vicinity of the target film thickness) as shown in FIG. 4 from the set film refractive index and the target film thickness. Is calculated for each of a plurality of wavelengths that can be selected in step S102. At this time, a graph of the primary differential coefficient or a graph of the secondary differential coefficient may be obtained as in the case of the quality determination by the film thickness value.

  Next, the calculation unit 47 determines the wavelength of the illumination light selected by the wavelength selection unit 45 based on the calculated characteristic of the reflectance change with respect to the change in film thickness (step S103). At this time, the wavelength at which the reflectance change is maximized in the vicinity of the target film thickness is selected. At this time, as in the case of the quality determination based on the film thickness value, the wavelength at which the primary differential coefficient is maximized may be selected, or the wavelength at which the secondary differential coefficient is zero may be selected. Good.

  As described above, when the wavelength of the illumination light is selected by the wavelength selection unit 45, the wavelength selection signal is output from the wavelength selection unit 45 and input to the illumination unit 21 via the control unit 50. When the wavelength selection signal from the wavelength selection unit 45 is input to the illumination unit 21, the dimming unit 23 selects a wavelength selection filter (not shown) corresponding to the wavelength selected by the wavelength selection unit 45 on the optical path. Insert into. This enables inspection with high sensitivity to changes in film thickness.

  When the wavelength of the illumination light is selected, the illumination light is irradiated onto the surface of the wafer W using the illumination system 20 as in the case of quality determination based on the film thickness value (step S104). Then, as in the case of quality determination based on the film thickness value, the imaging device 35 photoelectrically converts the image (regular reflection image) of the wafer W formed on the imaging surface to generate an image signal, and the image signal is converted into an image. The data is output to the processing unit 40 (step S105).

  The image processing unit 40 generates a digital image of the wafer W based on the image signal of the wafer W input from the imaging device 35, and inspects the film on the surface of the wafer W from the generated image information of the wafer W (step S106). At this time, the image processing unit 40 determines that the brightness value (signal intensity) of the image of the wafer W is normal if it is within a predetermined range, and determines that it is abnormal if it is out of the range. The luminance value (signal intensity) is calculated for each pixel in the image of the wafer W, and the presence or absence of a film defect (abnormality) over the entire surface of the wafer W (that is, non-uniformity in film thickness) is inspected. Is done. Further, the inspection result by the image processing unit 40 and the image of the wafer W at that time are output and displayed by an image display device (not shown).

  As described above, according to the present embodiment, the wavelength of the illumination light selected by the wavelength selection unit 45 is determined based on the characteristic of the reflectance change with respect to the film thickness change (that is, the change characteristic of the reflected light). It is possible to easily select an illumination wavelength that is highly sensitive to changes in thickness, and the film on the surface of the wafer W can be easily inspected with high sensitivity. At this time, if a wavelength at which the reflectance change (that is, the intensity change rate of reflected light) is maximized in the vicinity of the target film thickness is selected, a more sensitive inspection can be performed.

  If the inspection purpose is pass / fail judgment based on the film thickness value, the film thickness fluctuation range exceeds the adjacent peak or valley in the characteristic graph of the reflectance change with respect to the film thickness change under conditions where the film thickness fluctuation range is wide. Therefore, the film thickness cannot be calculated from the reflectance. Therefore, by selecting a longer wavelength from among wavelengths that provide constant sensitivity and constant linearity, the longer the wavelength, the longer the period (peak or valley) of the characteristic graph. The variation range can be covered.

  Further, even in the case of defect inspection with a simple inspection purpose, a wide variation range of film thickness can be covered by selecting a longer wavelength as in the case described above. On the other hand, when the purpose of inspection is simple defect inspection, even in the characteristic graph of reflectance change with respect to film thickness change, even under wide conditions where the fluctuation range of film thickness exceeds adjacent peaks or valleys Inspection is possible. Since it is extremely rare that a film thickness variation that is shifted by one period of the characteristic graph exists alone, if the peripheral portion and the film thickness data are compared, there is substantially no problem in the inspection.

  In the above-described embodiment, the wavelength of the illumination light is selected from among the wavelengths of the bright lines obtained from the mercury lamp, 313 nm, 365 nm, 405 nm, 436 nm, and 546 nm. However, the present invention is not limited to this. For example, if the illumination unit has a light source having a broad continuous wavelength and an optical system that can extract light of an arbitrary wavelength from such a light source, the optimum wavelength can be selected more reliably.

  Further, in the above-described embodiment, the wavelength at which the reflectance change is maximized in the vicinity of the target film thickness is selected in the characteristic graph of the reflectance change with respect to the film thickness change, but the present invention is not limited to this. You may make it select the wavelength from which the change of reflectance (namely, intensity change of reflected light) becomes the most linear change near thickness. In the characteristic graph, the position where the reflectance change is maximum (that is, the highest sensitivity) and the position having the best linearity substantially coincide with each other, but are accurately different. In addition, the center position when the range having good linearity is the widest is also different from these positions. The characteristic graph of the reflectance change is not a simple sine curve, for example, as shown in FIG. 3, but is an expression in which a multi-order term is added. is there.

  For this reason, a condition in which the change in reflectance is maximum (highest sensitivity) in the characteristic graph and a condition in which the linearity is the best may be used depending on the purpose of the inspection. For example, when the inspection purpose is pass / fail judgment based on the film thickness value, the wavelength with the best linearity is selected in the characteristic graph, and when the inspection purpose is simple defect inspection, the reflectance change is maximum in the characteristic graph. Can be selected.

  In the above embodiment, the film provided on the surface of the wafer W is inspected. However, the present invention is not limited to this. For example, the film provided on the surface of the glass substrate may be inspected. Is possible.

W wafer 1 Surface inspection device 10 Stage 20 Illumination system (irradiation part)
30 Light-receiving system 35 Imaging device (detection unit)
40 Image processing unit (inspection unit)
45 Wavelength selection unit 46 Input / output unit 47 Calculation unit 50 Control unit

Claims (10)

A stage that supports a substrate having a film provided on the surface; an irradiation unit that irradiates illumination light onto the surface of the substrate supported by the stage; and reflected light from the surface of the substrate that is irradiated with the illumination light. A detection unit for detecting, an inspection unit for inspecting the film from information on the reflected light detected by the detection unit, and a wavelength selection unit for selecting the wavelength of the illumination light from a plurality of preset wavelengths. An inspection method using an inspection device provided,
A setting step for setting a target film thickness and a refractive index of the film;
A calculation step of calculating a change characteristic of the reflected light with respect to a change in the film thickness in the vicinity of the target film thickness for each of the plurality of wavelengths from the set target film thickness and refractive index of the film,
And a determination step of determining a wavelength of the illumination light selected by the wavelength selection unit based on the calculated change characteristic. In the calculation step, from the set target film thickness and refractive index of the film, the intensity change rate of the reflected light with respect to the change in the film thickness in the vicinity of the target film thickness is calculated for each of the plurality of wavelengths.
2. The inspection method according to claim 1, wherein, in the determining step, a wavelength at which the intensity change rate of the reflected light is maximized is determined as a wavelength of the illumination light selected by the wavelength selection unit. In the calculation step, from the set target film thickness and refractive index of the film, the intensity change of the reflected light with respect to the film thickness change in the vicinity of the target film thickness is calculated for each of the plurality of wavelengths,
2. The inspection method according to claim 1, wherein, in the determining step, a wavelength at which the intensity change of the reflected light is the most linear change is determined as a wavelength of the illumination light selected by the wavelength selection unit. . A stage that supports a substrate having a film provided on the surface; an irradiation unit that irradiates illumination light onto the surface of the substrate supported by the stage; and reflected light from the surface of the substrate that is irradiated with the illumination light. A detection unit for detecting, an inspection unit for inspecting the film by measuring a film thickness of the film from information on the reflected light detected by the detection unit, and a plurality of preset wavelengths of the illumination light. An inspection method using an inspection apparatus including a wavelength selection unit that selects a wavelength,
A setting step for setting a target film thickness of the film, a complex refractive index of the film, and a complex refractive index of the substrate;
Based on the set target film thickness of the film, the complex refractive index of the film, and the complex refractive index of the substrate, the change characteristic of the reflected light with respect to the change of the film thickness in the vicinity of the target film thickness is determined for each of the plurality of wavelengths. A calculation step to calculate
And a determination step of determining a wavelength of the illumination light selected by the wavelength selection unit based on the calculated change characteristic. In the calculation step, from the set target film thickness of the film, the complex refractive index of the film, and the complex refractive index of the substrate, the intensity change rate of the reflected light with respect to the change of the film thickness in the vicinity of the target film thickness For each of the plurality of wavelengths,
5. The inspection method according to claim 4, wherein in the determining step, a wavelength at which the intensity change rate of the reflected light is maximized is determined as a wavelength of the illumination light selected by the wavelength selection unit. In the calculation step, from the set target film thickness of the film, the complex refractive index of the film, and the complex refractive index of the substrate, an intensity change of the reflected light with respect to the change of the film thickness in the vicinity of the target film thickness is calculated. Calculate for each of the plurality of wavelengths,
5. The inspection method according to claim 4, wherein, in the determining step, a wavelength at which the intensity change of the reflected light is the most linear change is determined as a wavelength of the illumination light selected by the wavelength selection unit. . An irradiation step of irradiating the surface of the substrate with illumination light using the illumination unit;
A detection step of detecting reflected light from the surface of the substrate irradiated with the illumination light using the detection unit;
An inspection step of inspecting the film from information of the reflected light detected in the detection step using the inspection unit;
In the inspection step, using the change characteristic calculated in the calculation step, the film is inspected by determining the increase or decrease in the film thickness from the intensity of the reflected light detected in the detection step. The inspection method according to any one of claims 1 to 6. An irradiation step of irradiating the surface of the substrate with illumination light using the illumination unit;
A detection step of detecting reflected light from the surface of the substrate irradiated with the illumination light using the detection unit;
An inspection step of inspecting the film by measuring the film thickness of the film from the information of the reflected light detected in the detection step using the inspection unit;
In the inspection step, the change characteristic calculated in the calculation step is used to calculate the film thickness from the intensity of the reflected light detected in the detection step, and the film is inspected based on the calculated film thickness. The inspection method according to claim 4, wherein the inspection method is performed. A stage for supporting a substrate provided with a film on the surface;
An irradiation unit for irradiating illumination light onto the surface of the substrate supported by the stage;
A detection unit for detecting reflected light from the surface of the substrate irradiated with the illumination light;
An inspection unit for inspecting the film from information of the reflected light detected by the detection unit;
A wavelength selection unit that selects a wavelength of the illumination light from a plurality of wavelengths set in advance;
The wavelength selector is
An input unit for inputting a target film thickness and a refractive index of the film;
An arithmetic unit that calculates, for each of the plurality of wavelengths, a change characteristic of the reflected light with respect to a change in the film thickness in the vicinity of the target film thickness from the target film thickness and refractive index of the film input to the input unit;
An inspection apparatus comprising: a determination unit that determines a wavelength of the illumination light selected by the wavelength selection unit based on the change characteristic calculated by the calculation unit. A stage for supporting a substrate provided with a film on the surface;
An irradiation unit for irradiating illumination light onto the surface of the substrate supported by the stage;
A detection unit for detecting reflected light from the surface of the substrate irradiated with the illumination light;
An inspection unit for inspecting the film by measuring the thickness of the film from the information of the reflected light detected by the detection unit;
A wavelength selection unit that selects a wavelength of the illumination light from a plurality of wavelengths set in advance;
The wavelength selector is
An input unit for inputting a target film thickness of the film, a complex refractive index of the film, and a complex refractive index of the substrate;
From the target film thickness of the film input to the input unit, the complex refractive index of the film, and the complex refractive index of the substrate, the change characteristic of the reflected light with respect to the change of the film thickness in the vicinity of the target film thickness A calculation unit for calculating a plurality of wavelengths;
An inspection apparatus comprising: a determination unit that determines a wavelength of the illumination light selected by the wavelength selection unit based on the change characteristic calculated by the calculation unit.

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