JP2007114087A - Surface inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface inspection method capable of detecting quickly and precisely an unevenness on a sample surface. <P>SOLUTION: This surface inspection method for inspecting a surface state of a wafer includes an irradiation process for emitting light from a prescribed position in a DMD 4 to irradiate the surface of the wafer W at a prescribed irradiation aperture angle, an image-focusing process for image-focusing reflected light on the surface of the wafer W by a telecentric optical system having an optical axis extended along a normal direction on the surface of the wafer W, a brightness data collecting process for picking up an image-focused image and for collecting a brightness data in each point on the surface of the wafer W, and a regulation process for changing an incident angle of the light to the each point on the surface of the wafer W and a reflection angle of the light from the each point, by switching a position of a mirror for projecting the light in the DMD 4, based on the brightness data, and for controlling the reflected light taken into a diaphragm 12 of the telecentric optical system to regulate sensitivity of the picked-up image. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface inspection method, and more particularly to a surface inspection method for inspecting the state of a sample surface.

  Conventionally, the inspection of the state of the sample surface is used for measuring the properties of the sample and determining the quality of the sample as a product. The inspection of the state of the sample surface is frequently used especially for the inspection of the unevenness of the sample surface used for manufacturing semiconductor devices.

  As a surface inspection apparatus used for such a surface inspection method, for example, Patent Document 1 discloses a light irradiation unit that irradiates a wafer surface with illumination light that is a parallel light beam, and illumination light that illuminates the wafer surface from an oblique direction of the wafer surface. An angle setting means capable of tilting the wafer surface so as to irradiate, the incident direction of the illumination light on the wafer surface and the optical axis match, and the wafer surface has a predetermined object-side opening angle with respect to one point on the wafer surface An object-side telecentric optical system that forms an image of the reflected light from the light source, an image pickup unit that picks up the formed image and collects luminance data, and frequency-resolves the luminance data by Fourier transforming the luminance data in a predetermined direction. A data conversion unit that extracts a predetermined frequency component from the frequency data obtained by the above and performs inverse Fourier transform, and obtains integral data of luminance data and the like in the measurement target region Surface inspection apparatus having a processing unit for determining the surface characteristics have been disclosed.

According to the surface inspection apparatus described in Patent Document 1, since the reflected light from the wafer surface is imaged at a luminance corresponding to the incident angle at each point on the wafer surface of the light from the light source, the angle setting means By adjusting the inclination of the wafer surface, it is possible to change the brightness of the wafer surface and adjust the detection sensitivity of the irregularities on the wafer surface.
JP-A-10-267636

  However, in the surface inspection apparatus described in Patent Document 1, it takes time to adjust the sensitivity because the inclination of the wafer surface is changed by the angle setting means when adjusting the sensitivity of the uneven portion of the wafer surface. In addition, there is a problem that advanced technology is required to control the tilt of the wafer surface.

  In addition, in the angle setting means provided in the surface inspection apparatus of Patent Document 1, since the inclination of the wafer surface only changes in the XY axis direction, the unevenness of the three-dimensional wafer surface is accurately determined with the luminance data in the biaxial direction. There was a problem that could not be grasped.

  An object of the present invention is to provide a surface inspection method capable of detecting unevenness of a sample surface at high speed and with high accuracy in a sample surface inspection used for manufacturing a semiconductor device.

  In order to solve the above-mentioned problem, the invention according to claim 1 is a surface inspection method for inspecting the surface state of a wafer, using spatial light modulation means for modulating output light of a light source according to pattern information, A telecentric optical system having an irradiation step of irradiating the surface of the wafer with a predetermined irradiation aperture angle by projecting light from a predetermined position in the spatial light modulation means, and an optical axis extending in a normal direction of the surface of the wafer An imaging process for imaging the reflected light of the surface of the wafer, a luminance data collection process for collecting the brightness data of each point on the surface of the wafer by capturing the imaged image, and the brightness data based on the brightness data By changing the light projection position in the spatial light modulator, the incident angle of light to each point on the surface of the wafer and the reflection angle of light from each point are changed. Characterized in that it comprises a an adjustment step of adjusting the sensitivity of the photographic image by controlling the reflected light taken into the diaphragm of the telecentric optical system.

  Here, the spatial light modulation means may be any means that modulates the output light of the light source according to the pattern information, and examples thereof include DMD and a reflective liquid crystal display element. Of these, the DMD is used as the spatial light modulation means.

  A second aspect of the invention is the surface inspection method according to the first aspect, wherein the spatial light modulation means is a DMD in which angle-variable mirrors are arranged side by side and the angles of the mirrors can be independently controlled. The adjusting step switches the position of a mirror that projects light in the DMD based on the luminance data.

  According to the first aspect of the present invention, the reflected light taken into the aperture of the telecentric optical system is changed by changing the light incident position and the reflection angle on the surface of the wafer by switching the light projection position in the spatial light modulator. The reflected light reaching the imaging surface of the imaging means such as a CCD can be adjusted by controlling the light. In this case, the amount of reflected light taken into the aperture of the telecentric optical system reflects the uneven state of the wafer. Thereby, it is possible to easily adjust the sensitivity of the captured image without changing the tilt of the surface of the wafer only by switching the light source in the surface light source.

  According to the second aspect of the present invention, by using the DMD as the spatial light modulation means, it is possible to switch the mirror that projects light in the DMD at high speed. Further, by switching at high speed not only in the biaxial directions of the XY axes but also in the oblique direction, it becomes possible to inspect the surface irregularities of the wafer at high speed and with high accuracy.

[Embodiment]
(overall structure)
A surface inspection apparatus 1 used in the surface inspection method according to the present embodiment includes an illumination optical system 2 (FIG. 1) and an imaging optical system 3 (FIG. 2).

(Detailed configuration)
The illumination optical system 2 irradiates the surface of the wafer W. The illumination optical system 2 is configured to include a DMD 4 as a spatial light modulator, a half mirror 5 and an objective lens 6, and the projection light from the DMD 4 is reflected by the half mirror 5 and passes through the objective lens 6 to be predetermined. The wafer is irradiated with an irradiation opening angle of. The objective lens 6 may be composed of a plurality of lenses. In the present embodiment, the object is a wafer W, and this wafer W is placed on a table (not shown).

  Here, the DMD 4 of the illumination optical system 2 will be described in detail. The DMD 4 is formed by laminating fine mirror elements on a semiconductor element in a lattice pattern, and each mirror independently has an inclination angle. By changing, projection of output light of a light source (not shown) can be turned on / off. A controller 7 (see FIG. 4) is electrically connected to the DMD 4 via a network or the like, and the position of the mirror that projects light in the DMD can be switched at high speed.

  Moreover, according to DMD4, as shown in FIG. 3, it becomes easy to switch the position of the mirror that projects light not only in the biaxial direction of the XY axis but also in the oblique direction. It becomes possible to inspect with higher accuracy.

  In addition, as a light source with which DMD4 is equipped, the well-known light source generally used for DMD can be used, For example, a metal halide lamp, an ultrahigh pressure mercury lamp, etc. can be used.

  In this embodiment, the DMD 4 is used as the spatial light modulation unit, but a reflective liquid crystal display element or the like may be used as the spatial light modulation unit.

  On the other hand, as shown in FIG. 2, the imaging optical system 3 focuses the reflected light from the surface of the wafer W on the CCD 10. The imaging optical system 3 includes a lens 8, a master lens 9, and a CCD 10, and the lens 8 is also used as the objective lens 6 described above. A data processing unit 11 (see FIG. 4) is electrically connected to the CCD 10.

  The master lens 9 is composed of a plurality of lenses. Among these, the lens 8 and a part of the master lens 9 constitute a telecentric lens. A diaphragm 12 is provided on the rear focal plane of the telecentric lens, and the telecentric lens and the diaphragm 12 constitute a telecentric optical system having an optical axis extending in the normal direction of the surface of the wafer W. With this telecentric optical system, the reflected light on the surface of the wafer W is imaged with a luminance corresponding to the incident angle (average incident angle) at each point on the surface of the wafer W.

  The CCD 10 is a photoelectric conversion element that receives light from the telecentric optical system and converts it into an electrical signal, and has an image plane on the optical axes of the lens 8 and the master lens 9. The CCD 10 outputs an electrical signal obtained by photoelectric conversion to the data processing unit 11 (see FIG. 4).

  The surface inspection apparatus 1 is connected to a control device 13 such as a personal computer via a network that can communicate with each other, and can transmit various instruction signals to each component of the surface inspection apparatus 1. It has become.

(Control configuration)
Next, FIG. 4 shows a control block diagram of the surface inspection apparatus 1 used in the surface inspection method according to the present embodiment.

  As shown in FIG. 4, the surface inspection apparatus 1 includes a control device 13. The control unit 14 included in the control device 13 includes a CPU (Central Processing Unit), a RAM (Random Access Memory) composed of a rewritable semiconductor element, and a ROM (Read Only Memory) composed of a nonvolatile semiconductor memory. The processing program recorded in the ROM is expanded in the RAM, and this processing program is executed by the CPU.

  As shown in FIG. 4, an input unit 15, a storage unit 16, a display unit 17, a controller 7 that controls the DMD 4, and a CCD 10 are connected to the control unit 14. A data processing unit 11 is connected to the CCD 10.

  The controller 14 adjusts the sensitivity of the CCD 10 at the time of photographing by the CCD 10 so that the controller 7 controls the DMD 4 as needed according to the surface properties of the wafer W. That is, the control unit 14 switches the position of the mirror that projects light in the DMD 4 as needed based on the luminance data transmitted from the data processing unit 11 according to the luminance of the captured image, under the control of the controller 7. Yes.

  For example, when the brightness of the uneven portion to be inspected in the captured image is higher than a predetermined reference value and the captured image of the uneven portion becomes white, as shown in FIGS. 5 and 6, a mirror that projects light in the DMD 4 Is moved in a predetermined direction by a predetermined distance so that a part of the light from the light source is not taken into the diaphragm 12, thereby reducing the ratio of the light reaching the CCD 10 and reducing the luminance of the photographed image. can do. On the other hand, when the brightness of the uneven portion to be inspected in the captured image is lower than a predetermined reference value and the captured image of the uneven portion becomes black, the position of the mirror that projects light in the DMD 4 is determined in another direction. By moving the distance by the distance and adjusting so that all the light from the light source is taken into the aperture 12, the ratio of the light reaching the CCD 10 can be increased and the brightness of the captured image can be increased.

  The input unit 15 includes a keyboard, a mouse, a touch panel, and the like, and a user can input instructions regarding the surface inspection of the wafer W.

  The storage unit 16 is a recording memory composed of a semiconductor memory or the like, and has a recording area for recording information input from the input unit 15. The storage unit 16 may be a built-in memory such as a flash memory, a removable memory card or a memory stick, or a magnetic recording medium such as a hard disk or a floppy (registered trademark) disk. .

  The display unit 17 is configured by a display or the like, and can display an inspection result or the like by the surface inspection apparatus 1. That is, by displaying a photographed image of the surface of the wafer W as an inspection result, the photographed image of the surface of the wafer W displayed on the display unit 17 is observed, and the presence / absence of the concavo-convex portion on the surface of the wafer W or the concavo-convex portion. The position can be measured.

  The controller 7 turns on a light source (not shown) included in the DMD 4 and controls the tilt angle of the mirror included in the DMD 4 based on an instruction signal from the control unit 14. Thereby, the controller 7 switches the position of the mirror which projects light in DMD4 at any time.

  The CCD 10 receives reflected light from the surface of the wafer W at a predetermined timing under the control of the control unit 14 and converts it into an electrical signal, and transmits the electrical signal to the control unit 14 as image data.

  The data processing unit 11 obtains the surface property of the wafer W based on the image data transmitted from the CCD 10. In addition, the data processing unit 11 of the present embodiment acquires luminance data of a captured image based on the image data and transmits it to the control unit 14.

(principle)
Next, the principle of the present invention will be described.

  The present invention utilizes the fact that when the position of the mirror that projects light in the DMD 4 of the surface inspection apparatus 1 is moved, an effect similar to that obtained by tilting the wafer surface can be obtained, the mirror that projects light in the DMD 4 can be obtained. The surface of the wafer W is inspected while changing the position and adjusting the sensitivity of the uneven portions on the surface of the wafer W.

  That is, first, in the state where the wafer W is not tilted by the surface inspection apparatus 1 of the present embodiment, as shown in FIG. 7, all the light from the light source is taken into the diaphragm 12 and 100% of the light reaching the CCD 10 from the DMD 4 It is.

  Next, assuming that the tilt of the wafer W is tilted by U / 2 degrees, as shown in FIG. 8, a part of the light from the light source is not taken into the diaphragm 12, and the light reaching the CCD 10 from the DMD 4 is 39.1%. Become. Here, “U degree” is an object-side opening angle of reflected light at one point on the surface of the wafer W.

  Furthermore, if the tilt of the wafer W is tilted by U degrees, the light from the light source is not taken into the diaphragm 12 as shown in FIG. 9, and the light reaching the CCD 10 from the DMD 4 becomes 0%.

  Next, when light is projected from the mirror located at the center of the DMD 4 in the surface inspection apparatus 1 of the present embodiment, all the projection light from the DMD 4 is taken into the diaphragm 12, as shown in FIGS. The light reaching the CCD 10 is 100%.

  Further, when the position of the mirror for projecting light in the DMD 4 is switched to a position moved D / 2 from the center of the DMD 4 in the X-axis direction, the incident angle shown in the illumination optical system in FIG. Light is irradiated to one point, light is reflected from one point on the surface of the wafer W at a reflection angle shown in the imaging optical system of FIG. 6, and the reflected light is imaged on the CCD 10. Here, “D” is the diameter of the mirror provided in the DMD 4. At this time, a part of the projection light from the DMD 4 is not taken into the diaphragm 12, and the light reaching the CCD 10 is 39.1%. That is, when the position of the mirror that projects light in the DMD 4 is moved by D / 2 in the X-axis direction, the same effect as that obtained by inclining the wafer by U / 2 degrees can be obtained.

  As described above, when the position of the mirror that projects light in the DMD 4 is moved to change the incident angle and the reflection angle of the light on the surface of the wafer W, the same effect as that obtained by tilting the wafer surface can be obtained.

  In the present invention, the surface inspection of the wafer W is performed based on the principle as described above.

  That is, in the surface inspection apparatus 1 of the present embodiment, the reflected light on the surface of the wafer W is imaged by the telecentric optical system with a luminance corresponding to the incident angle (average incident angle) at each point on the surface of the wafer W. . Therefore, when the photographed image of the surface of the wafer W as the inspection result is a dark image with low brightness, the incident angle at one point on the surface of the wafer W is changed by moving the position of the mirror that projects light in the DMD 4. By adjusting the reflection angle, the brightness of the surface of the wafer W is adjusted to be high. Thus, by moving the position of the mirror that projects light in the DMD 4 in accordance with the properties of the surface of the wafer W, it is possible to obtain a bright image with 100% luminance.

(Inspection method)
Next, the surface inspection method of the present invention using the surface inspection apparatus 1 will be described.

  When the controller 7 turns on the light source of the DMD 4 and light is projected from the DMD 4, the output light is reflected by the half mirror 5 and transmitted through the objective lens 6 as shown in FIG. Irradiate the top.

  Next, the light reflected by the surface of the wafer W is, as shown in FIG. 2, a telecentric optical system constituted by a telecentric lens constituted by a lens 8 and a part of the master lens 9 and a diaphragm 12. And is imaged on the CCD 10. At this time, the reflected light on the surface of the wafer W is imaged at a luminance corresponding to the incident angle at each point on the surface of the wafer W by the telecentric optical system.

  Subsequently, when the CCD 10 photoelectrically converts the reflected light on the surface of the wafer W and transmits the image data to the control unit 14, the display unit 17 displays a photographed image of the surface of the wafer W as an inspection result under the control of the control unit 14. indicate. As a result, a photographed image of the surface of the wafer W displayed on the display unit 17 can be observed, and the presence / absence of the uneven portion and the position of the uneven portion on the surface of the wafer W can be measured.

  On the other hand, the data processing unit 11 obtains the surface property of the wafer W based on the image data. In addition, the data processing unit 11 according to the present embodiment acquires luminance data of a captured image based on the image data and transmits the acquired luminance data to the control unit 14.

  Subsequently, based on the luminance data transmitted from the data processing unit 11, the control unit 14 switches the position of the mirror that projects light in the DMD 4 under the control of the controller 7 according to the luminance of the captured image. For example, when the brightness of the uneven portion to be inspected in the captured image is higher than a predetermined reference value and the captured image of the uneven portion becomes white, as shown in FIGS. 5 and 6, a mirror that projects light in the DMD 4 Is moved in a predetermined direction by a predetermined distance so that a part of the light from the light source is not taken into the diaphragm 12, thereby reducing the ratio of the light reaching the CCD 10 and reducing the luminance of the photographed image. can do. On the other hand, when the brightness of the uneven portion to be inspected in the captured image is lower than a predetermined reference value and the captured image of the uneven portion becomes black, the position of the mirror that projects light in the DMD 4 is determined in another direction. By moving the distance by the distance and adjusting so that all the light from the light source is taken into the aperture 12, the ratio of the light reaching the CCD 10 can be increased and the brightness of the captured image can be increased.

  As described above, the control unit 14 adjusts the sensitivity of the CCD 10 by setting the surface of the wafer W to an optimum luminance by controlling the DMD 4 as needed according to the surface property of the wafer W. The display unit 17 displays a captured image after adjusting the sensitivity of the CCD 10 under the control of the control unit 14.

  As described above, according to the surface inspection method of the present embodiment, the DMD 4 switches the light projection position, thereby changing the incident angle and the reflection angle of the light on the surface of the wafer W, so that the diaphragm 12 of the telecentric optical system can be used. The reflected light that is captured can be controlled to adjust the reflected light that reaches the imaging surface of the CCD 10. This makes it possible to easily adjust the sensitivity of the captured image without changing the tilt of the wafer surface, simply by switching the light source in the DMD 4.

  Further, by switching the projection position of light on the DMD 4 at high speed not only in the biaxial directions of the XY axes but also in the oblique direction, it becomes possible to inspect the irregularities on the surface of the wafer W at high speed and with high accuracy.

  In the present embodiment, the imaging optical system 3 is constituted by a double-sided telecentric optical system, but it can also be constituted by a one-sided telecentric optical system. In addition, the illumination optical system 2 of the present embodiment is configured to irradiate light through the lens 8 constituting the telecentric optical system together with the master lens 9 in the imaging optical system 3, but the projection light of the DMD 4 is a lens. By projecting through a half mirror or the like from a position closer to the wafer than 8, it is possible to irradiate light without going through the lens 8.

  In the present embodiment, the light projection position is switched by the spatial light modulation means. However, the light projection position is switched by controlling ON / OFF of the light source (LED) itself using an LED array or the like. It is good.

  As described above in detail, according to the surface inspection method of the present invention, it is possible to easily and accurately detect the unevenness of the sample surface in the sample surface inspection used for manufacturing a semiconductor device.

It is a figure which shows the illumination optical system which concerns on embodiment of this invention. It is a figure which shows the imaging optical system which concerns on embodiment of this invention. It is a top view which shows DMD which concerns on embodiment of this invention. It is a block diagram which shows the control structure of the surface inspection apparatus which concerns on embodiment of this invention. It is a figure which shows the illumination optical system at the time of moving the light source in the surface light source which concerns on embodiment of this invention. It is a figure which shows the imaging optical system at the time of moving the light source in the surface light source which concerns on embodiment of this invention. It is a conceptual diagram when the inclination of the wafer is 0 degree. It is a conceptual diagram at the time of making the inclination of a wafer into U / 2 degree. It is a conceptual diagram at the time of making the inclination of a wafer into U degree.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface inspection apparatus 2 Illumination optical system 3 Imaging optical system 4 DMD
5 Half mirror 6 Objective lens 7 Controller 8 Lens 9 Master lens 10 CCD
11 Data processing unit 12 Aperture 13 Control device 14 Control unit 15 Input unit 16 Storage unit 17 Display unit W Wafer

Claims (2)

A surface inspection method for inspecting the surface state of a wafer,
An irradiation step of using a spatial light modulation unit that modulates output light of the light source according to pattern information, projecting light from a predetermined position in the spatial light modulation unit, and irradiating the surface of the wafer with a predetermined irradiation aperture angle; An imaging step of forming an image of reflected light on the surface of the wafer with a telecentric optical system having an optical axis extending in the normal direction of the surface of the wafer; and imaging the formed image on the surface of the wafer Luminance data collection step for collecting the luminance data of each point, and the incident angle of light on each point on the surface of the wafer by switching the light projection position in the spatial light modulator based on this luminance data The sensitivity of the photographed image is adjusted by changing the reflection angle of the light from the point and controlling the reflected light taken into the aperture of the telecentric optical system. And an adjustment step of,
A surface inspection method comprising:   The spatial light modulation means is a DMD in which angle-variable mirrors are arranged side by side, and the angles of the mirrors can be independently controlled. In the adjustment step, the position of the mirror that projects light in the DMD based on the luminance data The surface inspection method according to claim 1, wherein the surface inspection method is switched.

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