JPH10206337A - Automatic visual inspection device for semiconductor wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently and accurately inspect forgetfulness of application of a resist, forgetfulness of separation or the like. SOLUTION: An automatic VISUAL inspection device of a semiconductor wafer is constituted by having a defect detecting optical system which radiates the illuminating light from an illuminating light source 6 to a surface of a semiconductor wafer placed in an inspecting position and obtains a detecting signal by performing light receiving processing on the reflected light from this surface by a detecting camera 7 and detecting signal processing system to automatically inspect and judge a defect in external appearance of a wafer surface from the detecting signal obtained by this defect detecting optical system, and has a signal correcting means to correct a detecting signal according to a change of the illuminating light from the illuminating light source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for determining whether or not a lithography step, an etching step, an ion implantation step, and the like in a semiconductor manufacturing process have been performed normally in these steps. For example, the present invention relates to an automatic semiconductor wafer appearance inspection apparatus for automatically inspecting / determining whether or not there is a defect in these operations to cause a defect on a wafer surface.

[0002]

2. Description of the Related Art Conventionally, inspections as to whether or not a lithography step, an etching step, an ion implantation step, etc. in a semiconductor manufacturing process have been performed normally have been performed.
It has been performed by inspecting a wafer surface for the presence or absence of defects by visual inspection of a skilled inspector using an apparatus equipped with visible light illumination and an optical microscope. Specifically, the wafer to be inspected is transported to the inspection position by the transport system, and at this position, the illumination light from the illumination light source is radiated to the wafer surface, and the reflected light is visually observed by the inspector to judge pass / fail (for defects). Or the like). When a defect is found in such an inspection, the found defect is confirmed using an optical microscope as necessary.

[0003] Defects on the wafer surface determined by such visual observation are of a type called a so-called macro defect. For example, exposure unevenness of each chip caused by defocusing of an exposure machine or the like. There are, for example, exposure failure, resist coating unevenness or forgetting to apply resist, resist peeling unevenness or forgetting to peel, and scratches or scratches in a CMP (Chemical-Mechanical Polishing) process performed for flattening the wafer surface.

By the way, the inspector who performs such a visual observation inspection naturally needs sufficient skill and experience. For example, when the wafer manufacturing process is changed due to the introduction of a new semiconductor wafer or the like. However, there is a problem that new inspection training is required in response to this change. For this reason, it has been conventionally considered that an inspection is automatically performed instead of a visual inspection by an inspector. For example, Japanese Patent Application Laid-Open No. 8-75661 discloses that the inspection is performed by human visual observation. A wafer defect detection device having a judgment function similar to the inspection capability is disclosed.

As described above, an automatic inspection apparatus has been proposed for the purpose of automating and labor-saving an artificial macro defect inspection such as a visual observation inspection by an inspector and improving a defect detection power. Such an apparatus irradiates the wafer with illumination light, detects reflected light from the wafer, for example, first-order diffracted light, and detects the presence or absence of a defect on the wafer surface from the detection signal. In this case, the detection signal of the primary diffraction light obtained by irradiating the non-defective wafer with the illumination light is stored in advance, and this is compared with the detection signal of the primary diffraction light from the wafer to be inspected. If there is, this is recognized as a defect, and is determined to be defective.

[0006]

In the inspection by such an inspection apparatus, defects such as uneven exposure due to defocus of an exposure device, uneven coating of resist, scratches, etc. are macro defects, Can be regarded as a local signal intensity change. For this reason, even if the illumination light intensity changes due to the deterioration of the illumination light source or the detected signal level of the wafer changes, the camera as the light receiving means is set so that the detection signal level always becomes a certain level. Can be compensated by performing gain control or AGC (Automatic Gain Control), or normalizing the contrast of the captured image.

However, in the case of inspecting the presence / absence of a resist over the entire surface of a wafer, such as the detection of forgetting to apply or peel off a resist, it is necessary to detect a difference in reflected light intensity level due to the presence / absence of a resist. . That is, in this case, a difference in the reflected light level over the entire wafer is detected instead of detecting a partial intensity change of the reflected light (first-order diffracted light) over the entire wafer. Therefore, if the gain control of the received light signal is performed as described above, there is no difference in the reflected light level, so that there is a problem that this inspection cannot be performed.
In particular, when the illumination light source is deteriorated, the intensity level of the illumination light is reduced and the reflected light level is also reduced. Therefore, based on the decrease in the reflected light level, it is said that, for example, there is forgetting to remove the resist. There is a problem that an incorrect judgment may be made.

The present invention has been made in view of such a problem.
In particular, it is an object of the present invention to provide an automatic semiconductor wafer appearance inspection apparatus capable of efficiently and accurately inspecting the presence or absence of a resist over the entire surface of a wafer, such as detection of forgetting to apply or peel off a resist. Aim.

[0009]

In order to achieve the above object, an automatic semiconductor wafer appearance inspection apparatus according to the present invention applies illumination light from an illumination light source to the surface of a semiconductor wafer placed at an inspection position. A defect detection optical system that irradiates and receives light reflected from the surface to obtain a detection signal, and automatically inspects and determines the appearance defect of the wafer surface from the detection signal obtained by the defect detection optical system. And a signal correction means for correcting the detection signal in accordance with the fluctuation of the illumination light from the illumination light source.

It is preferable that the defect detection optical system be configured to receive reflected light such as first-order diffracted light from the surface of the semiconductor wafer to obtain a detection signal. further,
It is preferable that the automatic appearance inspection apparatus according to the present invention be provided with a wafer transfer system for transferring the semiconductor wafer to the inspection position and a display / output system for displaying and outputting the inspection / judgment result in the detection signal processing system.

In the case of such an automatic visual inspection device,
Even when the illumination light amount fluctuates or decreases due to deterioration of the illumination light source, etc., the detection signal obtained by the defect detection optical system is corrected according to such fluctuation, so that the detection signal after correction is the same as before the fluctuation. This is equivalent to a detection signal based on the amount of illumination light. For this reason, even when detecting a difference in signal level (similar change in signal amplitude) from the entire surface of the wafer, such as an inspection for the presence or absence of a resist on the wafer surface, it is necessary to perform an accurate inspection by eliminating the influence of a change in the light source light amount. This makes it possible to reliably perform inspections for omissions in the resist coating process or the resist stripping process.

An illumination light amount detecting optical system for detecting the amount of illumination light from the illumination light source is provided separately from the defect detection optical system, and the signal correcting means responds to a change in the amount of illumination light detected by the illumination light amount detecting optical system. It can be configured to correct the detection signal. In any case, it is preferable that the signal correction unit is configured to adjust the gain of the detection signal in accordance with the fluctuation of the illumination light from the illumination light source.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the inside of an automatic appearance inspection apparatus according to the present invention as viewed from the front, and this apparatus is composed of a wafer transfer system, a defect detection optical system, a detection signal processing system, and a display / output system. . As described later, in this apparatus, the detection signal of the inspection wafer is compared with the detection signal of the reference wafer to inspect for the presence or absence of a defect. For this purpose, the reference wafer and the inspection wafer are moved by a vertical movement mechanism (not shown). It is set and held inside.

The wafer set in the vertical movement mechanism is mounted on a fork 3 attached to the arm 2 of the robot 1.
Are selectively or sequentially extracted and transferred to the wafer liner 4 to perform wafer alignment. After the alignment of the wafer is completed, the wafer 5 is transferred to the inspection position for diffracted light by the arm 2 of the robot 1 and stopped and held while being supported by the fork 3. The wafer transfer system is configured as described above. The figure shows a state in which the wafer 5 has been transferred to the inspection position for diffracted light.

When the wafer 5 is located at the inspection position, the planar illumination light source 6 for diffracted light inspection is turned on, and the surface of the wafer 5 is illuminated by the light from the illumination light source 6. Here, for example, as shown in FIG. 3, a plurality of linear patterns 31 are formed at a predetermined pitch on the surface of the wafer 5, and when this surface is irradiated with the illumination light A, the reflected light B is directly reflected. As well,
Diffracted light (eg, first-order diffracted light C, second-order diffracted light D, etc.) is generated. In this apparatus, the first-order diffracted light (more precisely, the -1st-order diffracted light) is detected by the detector 7.
The detector 7 uses a camera using a two-dimensional image sensor. The defect detection optical system is configured as described above.

The planar illumination light source 6 can collectively illuminate the entire surface of the wafer 5. At this time, the first-order diffracted light depends on the pattern pitch of the wafer 5 and the incident angle and wavelength of the illumination light from the planar illumination light source 6. Is determined, and the detection camera 7 is arranged in the emission direction of the first-order diffracted light. For this reason, although not shown, a mechanism for adjusting the mounting position of the planar illumination light source 6 and the detection camera 7 is provided in the present apparatus, and in the inspection on a mass production line, depending on the wafer to be inspected. The surface illumination light source 6 and the detection camera 7 are set to suitable positions before the start of the inspection (depending on the wafer pattern pitch or the like), and the inspection is performed in this state. The wavelength of the illuminating light is preferably a wavelength that does not adversely affect the semiconductor wafer due to exposure or the like, and for example, a monochromatic light of 550 nm is appropriate.

When the detection camera 7 detects the first-order diffracted light from the wafer 5 in this manner, as shown in FIG. 2, a diffracted light detection signal 20 from the camera 7 is input to a detection signal processing system. . Further, in the apparatus of the present invention, the photodetector 10 for detecting the light amount (intensity) of the illumination light from the planar illumination light source 6 is provided in the vicinity of the wafer 5 at the inspection position in a substantially same horizontal plane as the wafer 5. Is located. As the photodetector 10, for example, a photodiode is used. The light detector 10 detects fluctuations in the amount of light from the illumination light source 6, so that when the illumination light source 6 deteriorates and the amount of illumination decreases, this can be reliably detected. The illumination light amount detection signal 21 from the light detector 10 is also input to the signal processing system as shown in FIG.

Next, a signal processing operation by the detection signal processing system will be described. Diffracted light detection signal 20 from detection camera 7
Is first input to the AGC processing unit 23, and the illumination light amount detection signal 21 from the photodetector 10 is input to the signal level comparison unit 24 or the reference level generator 25.

In the inspection by the present apparatus, measurement is first performed using a non-defective non-defective wafer, and a reference image is obtained from the detection signal at that time and stored. Then, a surface image of the inspection wafer is obtained from a detection signal using the inspection wafer, and the presence / absence of a defect is inspected by comparing with a stored surface image (reference image) of a good wafer. For this reason, as shown in FIG. 2, two changeover switches 22a and 22b are provided in the detection signal processing system. These switches are switched to the broken line side during measurement using a non-defective wafer, and use an inspection wafer. During measurement, it is switched to the solid line side.

At the time of inspection, first, a non-defective wafer is transported and mounted at an inspection position, and the surface is irradiated with illumination light from a planar illumination light source 6. At this time, the AGC processing unit 23 operates as a buffer, and the diffracted light detection signal 20 detected by the detection camera 7 is sent to the image processing unit 26 as it is via the AGC processing unit 23. In the image processing unit 26, the analog signal sent in this way is converted into a digital signal, and thereafter, a predetermined image processing is performed to obtain a reference image signal. 27
Is stored. As can be seen from this, the reference image signal represents a diffracted light image of the wafer surface obtained when the non-defective wafer (wafer having no surface defect) is irradiated with the illumination light and the primary diffracted light is photographed by the detection camera 7. Things.

When the surface of the non-defective wafer is irradiated with the illumination light from the planar illumination light source 6, the light detector 10 detects the amount of illumination, and the detection signal 21 is input to the reference level generator 25. The detected light quantity at that time is stored in the reference level generator 25. As a result, the reference level generator 25 outputs a reference level signal corresponding to the light amount level stored in this way to the signal level comparison unit 24.

After setting the reference image and the reference level, an inspection wafer is transported and mounted at the inspection position in place of the non-defective wafer, and the surface thereof is irradiated with illumination light from the planar illumination light source 6. An automatic appearance inspection of the inspection wafer is performed. The diffraction light detection signal 20 obtained by detecting the primary diffraction light from the inspection wafer by the detection camera 7 is sent to the AGC processing unit 23. At this time, at the same time, the light amount detection signal 21 detected by the photodetector 10 is sent to the signal level comparison unit 24, where it is compared with the reference level signal sent from the reference level generator 25, and the difference between the two signals is calculated. In response, a gain control signal is output to the AGC processing unit 23.

For this reason, the diffraction light detection signal 20 of the inspection wafer input to the AGC processing unit 23 is subjected to gain adjustment based on the gain control signal sent from the signal level comparison unit 24 and then to the image processing unit 26. Sent. By performing such a gain adjustment, even when the illumination light amount changes due to the deterioration of the planar illumination light source 6 or the like, the diffracted light detection signal after the gain adjustment is a signal obtained based on the illumination light amount before the change. Is the same as That is, the fluctuation of the illumination light amount is compensated by the gain adjustment, and a diffracted light detection signal free from the influence of the fluctuation is obtained.

The diffracted light detection signal whose signal level has been compensated in the AGC processing unit 23 in this manner is
6, and after being subjected to digital conversion and predetermined image processing, is input to the defect detection processing unit 28. In the defect detection processing unit 28, the diffracted light detection signal input from the image processing unit 26 is compared with the image signal of a non-defective wafer input from the reference image memory 27, and the difference in the luminance level is determined for each pixel on the wafer surface. Is subjected to a determination process, and a defect inspection is performed. The inspection result is input to the display unit 29, processed as a display signal, displayed on a display (not shown), or output to a recording device.

Here, defects such as unevenness due to defocus of the exposure device, unevenness of resist coating, scratches, etc. are local defects when viewed from the entire surface of the wafer, and are regarded as partial intensity changes of the diffraction light detection signal. be able to. For this reason, even if the gain adjustment in the AGC processing unit 23 is not performed or is inaccurate, such a defect can be detected (however, more accurate detection can be performed by performing the gain adjustment).

On the other hand, when inspecting the presence / absence of the resist over the entire surface of the wafer, the intensity level of the reflected light from the illumination light source 35 differs between the case where the resist 38 is applied over the entire surface and the case where the resist 38 is not applied. When the illumination light amount fluctuates, it is not possible to determine whether the difference in the reflected light intensity level is caused by the presence or absence of the resist coating or the illumination light amount fluctuation, so that the presence / absence inspection of the resist cannot be accurately performed. There is a problem. For example, as shown in FIG. 4, when the resist 38 is applied to the wafer surface, the light 36a reflected by the surface of the resist 38 and the light 36b reflected by the wafer surface after passing through the resist 38 The signal strength detected by interference changes. In addition, this interference phenomenon changes according to the thickness of the resist.
In FIG. 4, the pattern profile on the wafer surface is omitted for simplicity of explanation, but since a resist is actually applied on the pattern, the combined detection of two phenomena due to diffracted light and interference is performed. The signal strength is measured.

Here, in the apparatus of the present invention, in the AGC processing unit 23, the gain of the diffracted light detection signal is adjusted in accordance with the fluctuation of the light amount of the illumination light source 6, so that the diffracted light detection signal after the gain adjustment is adjusted. The influence of the light quantity fluctuation of the illumination light source is eliminated. Therefore, only by comparing the intensity of the diffracted light detection signal after the gain adjustment with the reference signal, it is possible to accurately inspect the presence or absence of the resist.

When the defect inspection based on the first-order diffracted light is completed, the arm 2 of the robot 1 of the wafer transfer system is operated, and the inspection wafer 5 'is transferred to the scattered light inspection position shown by the broken line in FIG. . Thereafter, the scattered light detecting linear light source 8 is turned on, and light scattering from the surface of the wafer 5 'is detected by the detector 9. The detector 9 is composed of a camera, and a signal from the camera is input to an image processing device, and a defect is determined by scattering defect detection processing. However, since this part is not directly related to the present invention, a detailed description is omitted.

Another configuration of the apparatus shown in FIG. 1 will be briefly described. A clean unit 11 is provided at the upper part of the apparatus, and maintains the inside of the main body at the time of inspection in a clean environment. A control unit 13 constituting a signal processing system and a main body control system and a console 14 thereof are disposed in a control system rack 15 beside the rack body 12 constituting the housing of the present apparatus. The operator operates the apparatus based on the display information on the console 14 and
4 displays the state of the apparatus and the inspection results. An output monitor 16 dedicated to the image processing unit and a video printer 17 for outputting a hard copy of an image are also provided.

The inspection apparatus according to the present invention is not limited to the above. For example, although the wafer is held at the inspection position while being held by the fork 3 of the arm 2, the inspection position may be provided on the stage, and the wafer may be transferred onto the stage by the transfer system. In this case, , The photodetector is disposed on the stage. Furthermore, a half mirror and a simple condensing optical system may be used as a light amount detecting means of the illumination light source, so that a part of the light source may be guided to the photodetector. Further, as a light amount detecting means of another illumination light source, an optical fiber may be used to guide a part of the light source to the light detector. Since the incident end of the optical fiber can be arranged arbitrarily as long as it is around the light source, the degree of freedom of arrangement is large. Similarly, the photodetector can be arbitrarily arranged.

[0031]

As described above, according to the present invention,
It has a defect detection optical system that receives a reflected light from the surface of a semiconductor wafer to obtain a detection signal by receiving light, and a detection signal processing system that automatically inspects and determines a defect on the appearance of the wafer surface from the detection signal. Since there is a signal correction means for correcting a detection signal in accordance with the fluctuation of the illumination light from the illumination light source, even if the illumination light amount fluctuates or decreases due to deterioration of the illumination light source, the defect detection optical system Since the obtained detection signal is corrected according to such a variation, the corrected detection signal is equivalent to a detection signal based on the illumination light amount before the variation. For this reason, even when detecting a difference in signal level (similar change in signal amplitude) from the entire surface of the wafer, such as an inspection for the presence or absence of a resist on the wafer surface, it is necessary to perform an accurate inspection by eliminating the influence of a change in the light source light amount. This makes it possible to reliably perform inspections for omissions in the resist coating process or the resist stripping process.

[Brief description of the drawings]

FIG. 1 is an internal front view of a semiconductor wafer automatic appearance inspection apparatus according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of a signal processing system included in the inspection apparatus.

FIG. 3 is a schematic diagram showing illumination light and reflected light (diffraction light) of a wafer surface irradiated with a pattern.

FIG. 4 is a schematic view showing illumination light and reflected light applied to the surface of a resist-coated wafer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Robot 4 Wafer liner 5 Wafer 6 Planar illumination light source 7 Detection camera 10 Photodetector

Claims (5)

[Claims] 1. A defect detection optical system for irradiating illumination light from an illumination light source to a surface of a semiconductor wafer placed at an inspection position and receiving light reflected from the surface to obtain a detection signal, and a defect detection optical system. A semiconductor signal automatic inspection apparatus having a detection signal processing system for automatically inspecting and determining a defect on the appearance of the wafer surface from the detection signal obtained by the optical system; An automatic visual inspection apparatus for a semiconductor wafer, comprising: signal correction means for correcting the detection signal according to a change in illumination light. 2. The automatic appearance inspection apparatus according to claim 1, wherein the defect detection optical system receives a diffracted light from the surface of the semiconductor wafer to obtain a detection signal. 3. The apparatus according to claim 1, further comprising a wafer transfer system for transferring the semiconductor wafer to the inspection position, and a display / output system for displaying and outputting an inspection / judgment result in the detection signal processing system. 3. The automatic visual inspection device according to 2. 4. An illumination light amount detection optical system for detecting the amount of illumination light from the illumination light source is provided separately from the defect detection optical system, and the signal correction means detects the amount of illumination light detected by the illumination light amount detection optical system. The automatic appearance inspection apparatus according to claim 1, wherein the detection signal is corrected according to a change. 5. The automatic appearance inspection according to claim 1, wherein the signal correction unit adjusts a gain of the detection signal according to a change in illumination light from the illumination light source. apparatus.