JP2000338048A - Surface inspecting method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface inspecting method and apparatus capable of detecting a minute abnormal place. SOLUTION: The inspection position P on the surface of a semiconductor wafer 1 to be inspected is irradiated with pulse beam from a pulse laser 2 and scattered light generated by scattering when the inspection position P is an abnormal place due to refuse or a flaw is detected by a photodetector 3 using detection gate function. The emitting timing of the irradiation beam from the pulse laser 2 and the detection timing of the photodetector 3 using a detection gate are controlled by a timing synchronizing part 4 to turn the detection gate ON in matching relation to the arriving timing of scattered light to the photodetector 3 and, thereby, the influence of background light by the detection of noise is reduced to enhance the S/N ratio of the detection of scattered light being signal light to a large extent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface inspection method and an inspection apparatus for detecting and inspecting the presence or absence of abnormal spots such as dust and scratches on the surface of an inspection target such as a semiconductor wafer and a mask. .

[0002]

2. Description of the Related Art In semiconductor wafers, due to the miniaturization of processing dimensions of semiconductor devices formed on semiconductor wafers, there are severe restrictions on abnormal locations due to dust, scratches, etc. existing on the wafer, and usually, fine processing is performed. Only an abnormality whose size is about 1/5 to 1/10 or less of the dimensions is allowed. Therefore, a method of detecting these minute abnormal spots on a semiconductor wafer and inspecting the semiconductor wafer is important in improving the yield and reliability of semiconductor products and their manufacture.

As a method of detecting such an abnormality, a light detector detects scattered light from dust, scratches, or the like due to irradiation light from a predetermined light source as signal light.
There is a method for inspecting the presence or absence of an abnormality on a semiconductor wafer at an inspection position irradiated with irradiation light.

[0004]

SUMMARY OF THE INVENTION In semiconductor technology,
With the advance of fine processing technology, the miniaturization of processing dimensions is further progressing, but as the miniaturization progresses and the processing dimensions of micro processing become smaller, the size of abnormal spots such as dust on semiconductor wafers is also allowed Become smaller. For example, if a 1 Gbit memory can be manufactured in the future, the processing size is about 100 nm, and the size of the abnormal portion allowed at this time is about 20 nm or less. Such an abnormal portion is sufficiently smaller than the wavelength of the visible light, but when the abnormal portion to be detected is in a region smaller than the wavelength of the irradiation light, the intensity of the scattered light due to foreign matter such as dust has a diameter of about 6 mm. Therefore, the intensity of the scattered light rapidly decreases as the size of the abnormal portion decreases.

In this case, in order to perform an effective inspection on such a semiconductor wafer, it is necessary to establish a technique for detecting scattered light that is extremely weak light having extremely low intensity. However, in detection of such extremely weak light, background light due to detection of unnecessary noise light due to various factors other than the scattered light from the abnormal part becomes a problem.

For example, a part of the illuminating light is scattered by air molecules existing on the optical path to the inspection position of the semiconductor wafer to generate noise light, which is incident on and detected by a photodetector for detecting the scattered light. It becomes background light. If the abnormality on the semiconductor wafer to be detected is small, the S / N ratio decreases and the scattered light, which is extremely weak light, is buried in such background light, making it impossible to detect an abnormal part. Or detection takes a very long time.

[0007] By evacuating a predetermined portion of the inspection apparatus, it is also possible to reduce background light levels by excluding air molecules that cause scattering on the optical path. However, in this case, it is necessary to exhaust before the inspection, and to return to the atmospheric pressure again after the inspection, which complicates the inspection process and generates static electricity due to the movement of the air. This causes dust to be attracted to the semiconductor wafer. Further, background light caused by noise light from a mirror provided on the optical path of irradiation light cannot be excluded by applying a vacuum.

[0008] The above-mentioned problem similarly arises in the inspection of a surface other than a semiconductor wafer, such as detection of an abnormal portion on a mask surface for manufacturing a semiconductor device.

The present invention has been made in view of the above-mentioned problems, and it is possible to detect scattered light, which is extremely weak light, thereby making it possible to detect minute abnormalities existing on the surface of an inspection object. It is an object of the present invention to provide a surface inspection method and an inspection device capable of detecting a location.

[0010]

In order to achieve the above object, a surface inspection method according to the present invention is a surface inspection method for detecting an abnormal portion on a surface of an inspection object, and comprises a method of detecting a pulse light. A light irradiation step of irradiating a predetermined inspection position on the surface as irradiation light, and a light detection step of detecting scattered light generated when the irradiation light is scattered by an abnormal portion on the surface by predetermined detection means, The light detection step uses a detection gate synchronized with the irradiation timing of the irradiation light to the detection means, turns off the detection gate in a normal state, and suppresses detection of noise light serving as background light for scattered light detection. The detection gate is turned on at a predetermined timing and a time width in accordance with the arrival timing of the scattered light to the detection means to detect the scattered light.

A surface inspection apparatus according to the present invention is a surface inspection apparatus for detecting an abnormal portion on a surface of an inspection object, and emits pulsed light to irradiate a predetermined inspection position on the surface with irradiation light. A pulsed light source for irradiation, and a photodetector configured to detect scattered light generated by the irradiation light being scattered by an abnormal portion on the surface, and to control the timing and time width of the light detection by a detection gate. ,
Timing synchronization means for controlling the emission timing of the pulse light by the pulse light source and the detection timing of the scattered light by the light detector, wherein the timing synchronization means synchronizes the detection gate with the irradiation timing of the irradiation light. In the normal state, the detection gate is turned off to suppress the detection of noise light which is background light for scattered light detection, and the detection gate is set at a predetermined timing and time width in accordance with the arrival timing of the scattered light to the photodetector. The pulse light source and the photodetector are controlled so that the scattered light is detected as being turned on.

In the above-described surface inspection method and inspection apparatus, the irradiation light applied to the surface of the object to be inspected such as a semiconductor wafer or a mask is pulsed, and the means for detecting scattered light (for example, a photodetector) is used. By having a detection gate function, time-resolved measurement in light detection is enabled.

Further, in this configuration, the irradiation timing of the irradiation light and the detection timing of the scattered light are synchronized, and a detection gate such as a high-speed gate is turned on for a predetermined time width in accordance with the arrival timing of the scattered light, and the light detection is performed. To do. This suppresses deterioration of the S / N ratio of detection and inspection due to detection of unnecessary noise light other than scattered light to be detected as background light of inspection, and enables efficient detection of extremely weak light. As a result, it is possible to adopt a configuration in which a minute abnormal portion on the surface of the inspection target can be inspected efficiently in a shorter time.

Further, the surface inspection method includes the steps of: irradiating light which is present in a range which can be desired by the detecting means among all optical paths including an irradiating light path which is a light guiding path of irradiating light and a detecting light path which is a light guiding path of scattered light Alternatively, the number of pulsed light that is scattered light is always one or less at an arbitrary timing.

[0015] Alternatively, of all the light paths including the irradiation light path, which is the light guide path of the irradiation light, and the reflection light path, which is the light guide path of the reflection light reflected by the surface, the detection light means exists in a range that can be detected by the detection means. It is characterized in that the number of irradiation light or pulsed light that is reflected light is always one or less at an arbitrary timing.

Further, in the surface inspection apparatus, the pulse light source emits pulse light at a predetermined repetition frequency, and an irradiation optical path of irradiation light from the pulse light source to the surface inspection position and a light path from the surface inspection position to the photodetector. The optical path length in a range that can be desired by the photodetector among all the optical paths including the scattered light detection optical path is set to be shorter than the distance that light travels during one cycle of the repetition frequency.

Alternatively, the pulsed light source emits pulsed light at a predetermined repetition frequency, and further includes an optical terminator that terminates the optical path of the reflected light reflected by the surface from the irradiation light, from the pulsed light source to the inspection position on the surface. The optical path length of the range that can be expected by the photodetector in the total optical path including the irradiation optical path of the illumination light and the reflected optical path of the reflected light from the inspection position on the surface to the optical terminal end is the time of one cycle of the repetition frequency. Is set to be shorter than the distance traveled by light.

Of the light path combining the irradiation light path and the detection light path, or the light path combining the irradiation light path and the reflection light path, the light path portion within the range desired by the photodetector (detection means) tends to contribute to an increase in background light. Range. With respect to such an optical path range, the optical path length is set shorter than the distance corresponding to the time per one cycle of the repetition frequency of the irradiation light, and the number of the pulse lights simultaneously existing on the optical path is 1 at most. To be individual. At this time, for example, a pulse light corresponding to the next cycle, such as a condition that no noise light is generated due to scattering of pulse light other than the pulse light in the cycle that is actually involved in the abnormal point detection by air molecules or the like, Thereby, the background light can be further reduced.

Further, the surface inspection method may be characterized in that the number of pulse lights existing on all optical paths is always one or less at an arbitrary timing.

Further, the surface inspection apparatus may be characterized in that the optical path length of all optical paths is set shorter than the distance that light travels in one cycle of the repetition frequency.

The background light is further reduced by applying the above-described condition regarding the optical path length or the number of pulsed lights to the entire optical path without limiting to the range desired by the photodetector.

Further, regarding a specific configuration of the surface inspection apparatus, the photodetector has a streak tube for performing detection control by a detection gate by a predetermined gate operation or gate structure and generating a detection image from scattered light. It is good also as a characteristic that it is comprised.

Alternatively, the photodetector may be characterized by having an image intensifier for performing detection control by a detection gate by a predetermined gate operation and generating a detection image from scattered light. .

The above-described detection can be performed by using a gate structure for controlling a sweep voltage of a streak tube, a gate structure for cutting out a part of the sweep, or an image intensifier capable of performing a gate operation by applying a pulse voltage to the photodetector. A structure capable of controlling light detection by a gate can be employed.

The photodetector using the above-mentioned streak tube or image intensifier may be configured to further include a CCD for capturing a detected image for measuring the detected image. Alternatively, a configuration in which a photomultiplier tube for detecting a detection image is further provided can be employed.

Further, the photodetector may be characterized in that it has a photomultiplier tube for detecting scattered light by performing detection control by a detection gate by a predetermined gate operation.

Similarly, a photomultiplier tube capable of gate operation can be configured to be capable of controlling light detection by a detection gate.

Further, by placing the inspection object and driving the inspection object in the horizontal direction to move the inspection object,
It is characterized by further comprising a mounting table for performing an inspection on the entire surface of the inspection target.

Further, the mounting table is driven to move the inspection object by a distance shorter than the spot diameter of the irradiation light.

With this configuration, the entire inspection on the surface of the object to be inspected such as a semiconductor wafer can be sequentially inspected efficiently. Note that as a driving method in the horizontal direction, there are an XY scanning method, a rotary scanning method, and the like. Further, for the inspection of the entire surface, for example, the entire surface of the inspection target may be inspected by scanning the surface of the inspection target with irradiation light.

Further, the apparatus may be characterized in that it controls the entire apparatus including the pulse light source, the photodetector, and the timing synchronizing means, and includes control means for acquiring or analyzing detection data by the photodetector.

Further, the apparatus may further include a display unit connected to the control unit for displaying operation information on each unit of the apparatus or inspection information based on a detection result.

By providing a control means such as a computer or a display means such as a display, it is possible to control the entire apparatus, to instruct / specify the operating conditions of each part of the apparatus, and to perform the detection result. It is possible to adopt a configuration in which the information is displayed on the display means so that the inspector can visually determine the presence / absence and position of the abnormal part based on the display.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a surface inspection method and an inspection apparatus according to the present invention will be described below in detail with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional ratios in the drawings do not always match those described. In addition,
In the following, "scattered light" is a light component in which irradiation light is scattered in various directions including directions other than the reflected light path from an abnormal portion such as dust or a scratch on the surface of an inspection target such as a semiconductor wafer or a mask. A light component that can be used as signal light for detecting an abnormal point, and light such as irradiation light or reflected light that is scattered from air molecules or the like on the optical path, etc., is referred to as noise light or background light. Scattered light.

FIG. 1 shows a first embodiment of the surface inspection apparatus according to the present invention.
1 is a configuration diagram schematically illustrating a semiconductor wafer inspection device according to an embodiment. A semiconductor wafer 1 to be inspected is mounted and fixed at a predetermined position on a wafer mounting table 10 which is an XY stage movable in a horizontal direction (X and Y directions).

In the present embodiment, pulsed light emitted from a pulsed laser 2 as a pulsed light source at a predetermined repetition frequency is used as irradiation light applied to the surface of the semiconductor wafer 1. The pulse light generated and emitted by the pulse laser 2 is reflected by a reflection mirror 21 for converting an optical path to a predetermined inspection position on the surface of the semiconductor wafer 1.
Through the irradiation optical path l ₀ , and the irradiation angle θ
Irradiates the semiconductor wafer 1 from an oblique direction.

At this time, when the inspection position on the surface of the semiconductor wafer 1 (indicated by the symbol P in the figure) is not an abnormal place where dust, scratches, etc. are present, but a normal flat place, The irradiation light is a reflection light normally reflected by the semiconductor wafer 1 and has a reflection angle θ equal to the irradiation angle described above.
In emitted by the reflection optical path l _2.

[0038] The reflected light is trapped by a light trap 5 disposed as a light end of the reflection optical path l ₂ at a predetermined position on the reflection optical path l _2. Note that this optical trap 5
Is formed in a cone shape, the inner surface of which is formed as a mirror, and is formed and installed so that the reflected light from the semiconductor wafer 1 incident via the reflected light path l ₂ does not return to the outside of the optical trap 5 again. With respect to the reflected light, the configuration in which the optical trap 5 is provided as the optical terminal portion as described above reliably excludes the reflected light and suppresses the generation of noise light.

On the other hand, if the inspection position P on the surface of the semiconductor wafer 1 is an abnormal place where dust or scratches are present,
Irradiation light thereof and part thereof is scattered in the direction other than the reflected light path l ₂ resulting in scattered light. By detecting such scattered light generated by the abnormal portion, it is possible to detect and inspect the presence or absence of the abnormal portion on the surface of the semiconductor wafer 1 and its position.

The scattered light is detected by the photodetector 3. The photodetector 3 has a function of a detection gate capable of controlling a timing and a time width for performing photodetection by using a gate operation by controlling a voltage applied to each unit or a gate structure using a control plate or the like. It is configured.

In the present embodiment, the light detector 3 is
It is composed of a leak tube 31 and a CCD 32,
Light path₀And reflected light path l_TwoSpatially separated from the above
Predetermined for the inspection position P on the surface of the semiconductor wafer 1
(For example, vertically above, in the Z direction).
Thereby, the irradiation light on the surface of the semiconductor wafer 1 is irradiated.
Of the scattered light from the abnormal location at the inspection position P
Detection optical path l vertically above ₁Light components scattered in the direction
It is detected by the output unit 3. Also, on the semiconductor wafer 1
Scattered light from the abnormal point P to the photodetector 3
In order to increase the detection efficiency by guiding and condensing light, for example,
A converging mirror 30 having a circular shape or the like is provided. What
Incidentally, a specific detection gate machine of the photodetector 3 having this configuration.
Noh will be described later.

The timing synchronizing section 4 controls the emission timing of the pulse light to be the irradiation light from the pulse laser 2 and the light detection timing by the detection gate in the photodetector 3. In the present embodiment, the timing synchronization unit 4 is configured to include a timing adjustment unit 41 and a sweep control unit 42. For example, the timing synchronization unit 4 is controlled based on a pulse light emission trigger signal from the pulse laser 2.
In 1, the timing (the phase in the case of the repetitive operation) is adjusted, and the swept operation by the application of the sweep voltage to the streak tube 31 is controlled via the sweep control unit 42 by the adjusted timing. Thus, the timing of the detection gate for detecting the scattered light in the photodetector 3 is controlled in synchronization with the timing of emitting the irradiation light in the pulse laser 2.

The operation and drive of the pulse laser 2, the photodetector 3, the timing synchronizing section 4, and the wafer mounting table 10 are further controlled by a control section 6 using, for example, a personal computer. The control unit 6
May acquire and process measurement data from the photodetector 3 and, if necessary, display the measurement results and measurement conditions on a display unit 7 such as a display. The control unit 6 may be connected to an input unit such as a keyboard and an instruction panel for designating detection conditions and instructing execution of an inspection. Further, a storage device for storing data may be further connected.

The operation of the semiconductor wafer inspection apparatus according to the above embodiment, the semiconductor wafer inspection method thereby, and its effects will be described.

FIG. 2 is a schematic diagram for explaining the operation and the like of the present semiconductor wafer inspection apparatus (inspection method). First, with reference to FIG. 2A, a problem of a conventional apparatus in a semiconductor wafer inspection apparatus utilizing detection of scattered light from an abnormal portion will be described. Irradiation light emitted from the light source 2a such as CW laser is irradiated to a predetermined inspection position P on the surface of the semiconductor wafer 1 by irradiating the optical path l _0. At this time, if the inspection position P is an abnormal location, part of the irradiation light is scattered by dust or scratches at the abnormal location,
The scattered light, which is the signal light, is detected by the photodetector 3a.

At this time, apart from the scattered light from the abnormal part, noise light is generated due to unnecessary scattering from each part, and this noise light enters the photodetector 3a and becomes background light for detection / inspection. As a result, the accuracy and efficiency of abnormal point detection deteriorate. As examples 2 (a), the irradiation by dirt and noise light resulting from the irradiation light, such as by disturbances of the reflecting surface, air molecules point P ₂ on the illumination optical path l ₀ at the reflection point P ₁ on the reflecting mirror 21 noise light resulting from the light, and the noise light generated from the reflected light by air molecules point P ₃ on the reflection optical path l ₂ are shown. A part of the noise light enters the photodetector 3a and becomes a background light for detection.

The above-mentioned generation of noise light and background light becomes a problem particularly as the processing dimensions of the semiconductor device become finer and the allowable size of abnormal portions such as dust and scratches becomes smaller. That is, in a region where the detection target is smaller than the wavelength of the irradiation light, the intensity of the scattered light is proportional to the sixth or fourth power of its size and diameter. The intensity of the scattered light to be reduced rapidly decreases.

On the other hand, the intensity of the noise light does not change if the irradiation light intensity and the device configuration are the same. The ratio deteriorates rapidly. in this case,
Since scattered light cannot be detected or averaging must be performed by performing a large number of measurements to separate and discriminate scattered light from background light, long inspection times It becomes necessary to perform measurement and detection,
The efficiency of the inspection process is greatly reduced.

In the background light described above, scattering noise light due to air molecules on the optical path is particularly problematic. On the other hand, it is conceivable to evacuate the device portion including each optical path, but in this case, the inspection process or the inspection device becomes complicated due to the exhaust before the inspection and the process of returning to the atmospheric pressure after the inspection, and also the exhaust. At the time, the movement of the air causes a problem that dust is adsorbed due to the generation of static electricity. In addition, noise light caused by a mirror or the like cannot be excluded by applying a vacuum.

FIGS. 2B and 2C show a semiconductor wafer inspection method according to the above embodiment for solving such a problem. Here, the pulsed laser 2 is used as a light source for generating irradiation light, and the irradiation light is pulsed light. In addition, a photodetector that detects scattered light from an abnormal location is a photodetector 3 having a detection gate function. Here, in the figure, the detection gate of the photodetector 3 and its O
N / OFF is conceptually indicated by the gate G and its opening and closing.

The irradiation light emitted from the pulse laser 2 as the irradiation light is guided to the semiconductor wafer 1 by the irradiation light path ₁₀ . At each position of the irradiation optical path l ₀ At this time, noise light is generated due to scattering from air molecules such as illustrated for the point P ₄ in FIG. 2 (b), the part of which reaches the photodetector 3 . The noise light that has reached the photodetector 3 is not detected at this timing because the photodetector 3 closes the gate G (detection gate is OFF) and does not contribute to the background light for detection.

When the inspection position of the semiconductor wafer 1 is at an abnormal point P
If there is, the irradiation light is normally reflected by the semiconductor wafer 1.
The reflected light path l_TwoApart from the light reflected by
Are scattered by the abnormal portion P and become scattered light. This
Detecting optical path l₁The scattered light component scattered in the direction is shown in FIG.
As shown in (c), the light reaches the photodetector 3 (detection light path l).
₁Upper point P_Five). At this time, the light detector 3 detects the scattered light.
Gate G is opened at the arrival timing (detection gate
And the scattered light is detected. In addition, light detection of scattered light
When the light arrives at the container 3, the reflected light is reflected light path l shown in the figure._Two
Upper point P₆Has been reached.

In the present embodiment, as shown in FIG. 2B, the detection gate of the photodetector 3 is turned off when light detection is not required, such as when illuminating light is guided. 3 is not detected as background light for detection, and when the inspection position P on the surface of the semiconductor wafer 1 is abnormal as shown in FIG. At the timing when the scattered light arrives at the detection gate, the detection gate is turned on to detect the scattered light. By configuring and controlling the photodetector 3 and its operation in this way, the background light level with respect to the scattered light is significantly reduced, the detection efficiency (S / N ratio) is improved, and the measurement time required for detection is measured. Can be shortened and the inspection can be speeded up.

The improvement of the S / N ratio by the detection of the scattered light using the detection gate whose detection timing is synchronized is as follows.
It becomes possible for the first time by using a pulse light source such as a pulse laser that generates pulse light instead of a continuous light source such as a CW laser as the light source. That is, the irradiation light is pulsed light, and the light detection is ON / O by the detection gate.
By performing FF and controlling them synchronously, efficient scattered light detection such as time-resolved measurement with high time resolution is realized.

The synchronization and control of the timing between the pulse laser 2 and the detection gate of the photodetector 3 are performed by the timing synchronization section 4 (not shown in FIG. 2) shown in FIG. ON / OFF of detection gate so that light is efficiently detected under good S / N conditions
Is controlled. The operation control timing of the detection gate, the optical path length of the illumination optical path l ₀ and the detection optical path l ₁ is predetermined by the device configuration, this known optical path length and the pulsed light from the pulsed laser 2 (irradiation light) The arrival timing of the scattered light to the photodetector 3 is determined from the emission timing of the light, and the detection gate is turned on by this timing.
As N, scattered light is detected. Such timing control enables reliable timing synchronization and efficient scattered light detection.

[0056] In addition, the scattered light of the light detector irradiating light path upon reaching the 3 l ₀ · reflection optical path l irradiation light for generating _second upper like other pulse light (scattered light to be detected, before and after When there are further adjacent cycles of irradiation light / reflection light, there is a possibility that when the detection gate is turned on, noise light from them is simultaneously detected as background light.

On the other hand, in the present embodiment, with respect to the repetition frequency of the pulse light emission of the pulse laser 2 and the optical path length of each optical path, the irradiation optical path l ₀ from the pulse laser 2 to the inspection position P of the semiconductor wafer 1, The optical path length of the entire optical path including the detection optical path l ₁ from the inspection position P to the photodetector 3 is determined by the distance that light travels during a time interval (one cycle time) corresponding to the repetition frequency of the pulse laser 2. It is set shorter than

With such a configuration, the time difference between the emission of the irradiation light from the pulse laser 2 and the detection of the scattered light by the photodetector 3 becomes shorter than the time interval of one cycle of the repetition frequency. as shown in c), absent the pulse light other than the scattered light in the total optical path at the time of the scattered light detected combined irradiation optical path l ₀ and the detection optical path l _1, FIG. 2
At any timing other than the timing shown in (c), only one or less pulse light always exists on this entire optical path.

Also, on the optical path combining the irradiation optical path l ₀ and the reflected optical path l ₂ , in FIG. 2C, other than the scattered light, pulse light other than the reflected light reaching the point P ₆ exists. do not do. Therefore, the presence of pulsed light due to the period before and after the scattered light to be detected greatly suppresses noise light generated from scattering by air molecules and the like, so that background light due to the noise light can be reduced. And the detection efficiency can be further improved.

As for the optical path length, the irradiation optical path l ₀ from the pulse laser 2 to the inspection position P of the semiconductor wafer 1 and the reflection optical path l ₂ from the inspection position P to the optical trap 5 are further described.
It is preferable to set the optical path length of all the optical paths, including the above, to be shorter than the distance that light travels during a time interval (one cycle time) corresponding to the repetition frequency of the pulse laser 2. This can be for the whole of the irradiation optical path l ₀ and the reflection optical path l _2, it is possible to always 1 or less pulsed light exist simultaneously, further to suppress the generation of the noise light.

With respect to the conditions regarding the repetition frequency, the optical path length, and the number of pulse lights, specifically, for example, when the repetition frequency of the pulse laser 2 is set to 100 MHz, the time interval of the pulse light emission is 10 nsec. By setting the irradiation light path and the detection light path, or the light path length combining the irradiation light path and the reflection light path shorter than the distance 3 m corresponding to the above, the pulsed light is emitted at an arbitrary time on the entire light path portion combining the two light paths. 1
It can be configured such that there are no more than the number.

Further, it is particularly preferable in terms of suppression of noise light that the configuration satisfies both of the above-described two conditions relating to the irradiation light path and the detection light path for the light path and the light path length, or the irradiation light path and the reflection light path. Furthermore, the above condition regarding the optical path length or the number of pulsed light is not applied to the irradiation light path and the detection light path, or to the light path portion desired by the photodetector 3 in the entire light path, but not to the entire light path combining the irradiation light path and the reflection light path. May be applied. Such a range is a range in which the generated noise light easily contributes as the background light, and the noise light and the background light can be reduced even under such conditions.

The state in which the detection gate is turned off other than when the scattered light reaches the photodetector 3 is not necessarily limited to the case where the photodetector 3 does not perform any light detection. Is performed, but is not in a state that satisfies certain conditions used as data, such as being within a predetermined area of a detected image to be generated. (That is, light detection is performed but scattered light detection is turned off).

The time width during which the detection gate is turned on may be appropriately set in accordance with the configuration of the apparatus and the intensity of noise light. For example, in order to ideally cut out scattered light as signal light, a minute abnormal Within the time when light spreads over the entire area (0.1 fs if the diameter of the abnormal area is 30 nm)
(about ec or more), the shorter the better.

Incidentally, a method and an apparatus for detecting foreign matter in which scattered light is detected in a time-division manner are disclosed in Japanese Patent Application Laid-Open No. 3-102249. However, the method and apparatus relate to a patterned wafer, wherein the scattered light from the two illuminations is measured in a time-sharing manner by the same detector in order to prevent the displacement of the detector, and according to the present invention. The purpose is different from the inspection method and apparatus. The configuration is also time-divisional on the circuit by the output sample-and-hold, and the detector itself does not have a gate function, and the reduction of the background light can be achieved by such time-divisionalization. Can not.

The above-described detection gate function in the photodetector 3 shown in FIG. 1 will be described. In the present embodiment, the photodetector 3 is constituted by the streak tube 31 and the CCD 32, and the detection gate function is realized by the gate operation or the gate structure of the streak tube 31.

FIG. 3A shows an example of the structure of the streak tube 31. Here, light (scattered light) incident on the streak tube 31 is photoelectrically converted at the photoelectric surface 311 to generate photoelectrons. The traveling direction of the photoelectrons is deflected by a deflection electrode 312 to which a predetermined sweep voltage is applied, and is amplified and multiplied by an MCP (micro channel plate) 313. A detection image is formed at the position. The formed detection image is detected and imaged by the CCD 32 connected to the fluorescent screen 314.

In the streak tube 31, the light detection is time-resolved by the sweep of the photoelectrons by the sweep voltage applied to the deflection electrode 312. The sweep timing and the sweep voltage waveform are controlled by the sweep control of the timing synchronization unit 4. Part 4
The detection gate function can be realized by synchronizing the scattered light with the arrival timing at the photodetector 3 by means of 2.

For example, based on the emission timing of the irradiation light from the pulse laser 2 and the arrival timing of the scattered light obtained from each optical path length, the image detected by the scattered light is shifted to the center position of the fluorescent screen 314 in the sweep direction. By controlling the sweep timing by the sweep voltage so as to form an image on the detection gate, ON / OF of the detection gate using time-resolved measurement is performed.
By realizing F, it is possible to detect the scattered light separately from the background light. At this time, it is also possible to select suitable conditions for the sweep time width, which is the time required for the sweep, and the sweep waveform, by appropriately setting the configuration of each part of the streak tube, the required time resolution, and the like. it can.

When the scattered light is extremely weak light,
The synchronized detection gate operation is performed a plurality of times for each inspection position on the semiconductor wafer 1 according to the repetition frequency of the irradiation light from the pulse laser 2 (for example, by a method such as a synchro scan streak), and the results are integrated or By averaging, the detection S / N ratio can be further improved. For example, when the repetition frequency is 100 MHz and the inspection time required for a specific inspection position is 500 μsec, the number of possible integrations is 50,000.

Further, the inspection of the entire semiconductor wafer 1 is performed by sequentially performing such detection and measurement for each inspection position. In the embodiment shown in FIG. 1, the wafer mounting table 10 is an XY stage that is movable in the horizontal direction (X direction and Y direction), whereby the semiconductor wafer 1 is moved in the horizontal direction and each position is sequentially moved. Inspection position. In this case, the driving method of the wafer mounting table 10 is such that the semiconductor wafer 1 is inspected by a distance (for example, about several μm) shorter than the spot diameter of the irradiation light, which is pulse light, in order to surely inspect the whole of the semiconductor wafer 1. It is preferable to drive to move 1. Further, as such a wafer mounting table, it is also possible to use a wafer table that performs rotational scanning.

Further, the spot shape of the irradiation light applied to the surface of the semiconductor wafer 1 is set as a line extending in a direction perpendicular to the sweep direction of the streak tube 31, and each position within the linear spot is defined. The inspection may be performed at the same time. At this time, the detection image generated by the streak tube 31 is a two-dimensional image in which one axis corresponds to time information by sweeping and the other axis corresponds to position information by a linear spot.

The determination of the presence / absence of an abnormal portion such as dust and scratches from the luminance distribution of the scattered light image picked up and detected by the CCD 32 and the determination of the position are displayed on the display unit 7 via the control unit 6, for example. The inspector may visually perform the detection / inspection result based on the detected / inspection result, or perform image processing / data processing in the control unit 6 or a computer connected thereto, and thereby detect an abnormal portion. It is also possible.

The CCD 32 connected to the streak tube 31 and detecting the detected image is, for example, a cooled CCD.
, The detection noise can be further reduced. Alternatively, an EB-CCD (electron incidence type CC)
D) may be used. Although the MCP 313 for electronic amplification is provided in the streak tube 31 shown in FIG. 3A, amplification is not performed in the streak tube 31 and an amplification function by the MCP is provided between the streak tube 31 and the CCD 32. An image intensifier having the above may be further installed.

Further, with respect to the output of the streak tube 31,
A configuration in which a photomultiplier tube (PMT) is connected instead of the CCD 32 to detect a detection image is also possible. In this case as well, the device configuration is the same as that of FIG. 1, but the detection is not performed when the spot shape is linear.

In the streak tube 31, the time resolution is performed as spatial separation by sweeping electrons, so that detection is performed by gate operation such as voltage application (in this embodiment, application of a sweep voltage to the deflection electrode 312). Not only the gate but also the detection gate using the gate structure of the streak tube 31 is possible. FIG. 3B shows an example of such a gate structure.

In the streak tube 31, an aperture plate 315 is provided between the deflection electrode 312 and the MCP 313. The aperture plate 315 has an opening 31 having a predetermined shape and area such as a circle at the center thereof.
5a are formed, and this allows the opening 31
A gate structure for detecting and imaging only the electrons that have passed through 5a is configured, so that the S / N ratio can be further improved in combination with the above-described control using the sweep voltage.

In addition to the above, usually, acceleration of electrons
Set the voltage of each part so that amplification is not performed,
For example, a gate operation by applying a pulse-like gate voltage for enabling acceleration and amplification of electrons and turning on a detection gate to respective portions such as the photoelectric surface 311, the MCP incident surface 313a, and the MCP exit surface 313b is also possible. , A detection gate can be realized.

FIG. 4 is a configuration diagram schematically showing a second embodiment of a semiconductor wafer inspection apparatus which is a surface inspection apparatus according to the present invention. In the present embodiment, the photodetector 3 is an image intensifier 33 such as a proximity type and a CCD.
34. Further, in response to the use of the image intensifier 33 instead of the streak tube 31, the timing synchronization unit 4 applies a gate voltage and the like described later to the timing adjustment unit 41 and the image intensifier 33. It has a voltage control section 43.

As the image intensifier 33, one having a gate operation function is used to realize a detection gate. As such an image intensifier 33, for example, there is one in which a microstrip line is provided on a photocathode (see Japanese Patent Publication No. 4-77505 and Japanese Patent Laid-Open Publication No. 5-308550). this is,
A gate for switching ON / OFF of detection by applying a pulse voltage to a microstrip line by a predetermined pulse voltage generator (in the embodiment shown in FIG. 4, for example, included in the voltage control unit 43). Perform the operation. In particular, an image intensifier using a microstrip line has a high time resolution of its gate operation, and is preferable as a detection gate.

In addition to the above, a gate operation is performed by another method or structure such as controlling the acceleration / amplification of electrons by applying a pulse voltage to each part such as a photoelectric surface or an incident surface of an amplifier such as an MCP. May be used. Further, as in the case of the embodiment shown in FIG. 1, a configuration in which a photomultiplier tube is connected instead of the CCD 34 to detect a detection image is also possible.

FIG. 5 is a block diagram schematically showing a third embodiment of a semiconductor wafer inspection apparatus which is a surface inspection apparatus according to the present invention. In the present embodiment, the photodetector 3 includes a photomultiplier tube 35, and the operating voltage of the photomultiplier tube is controlled by a voltage control unit 44 of the timing synchronization unit 4.

As the photomultiplier tube 35, a photomultiplier tube having a gate operation function is used to realize a detection gate. An example of such a photomultiplier tube 35 is an MCP-PMT with a high-speed gate. Further, as for the structure or the like for realizing the gate operation, the same method and structure as those for the above-described image intensifier can be used, such as installation of a microstrip line on the photocathode.

FIG. 6 is a block diagram schematically showing a fourth embodiment of a semiconductor wafer inspection apparatus which is a surface inspection apparatus according to the present invention. The device configuration of this embodiment is the same as that shown in FIG. 1, but the irradiation light is partially branched by a half mirror 22 installed at a predetermined position on the irradiation light path ₁₀ . On the other hand, the timing synchronizing section 4 has a branch light detector 40, and determines the irradiation light emission timing by detecting the irradiation light component branched by the half mirror 22 with the branch light detector 40. Then, based on this, the detection gate of the photodetector 3 is controlled. However, in such a configuration, a high-speed photodetector such as an avalanche photodiode or a PIN photodiode is used in order to quickly respond to a trigger signal.

The surface inspection method and the inspection apparatus according to the present invention are not limited to the semiconductor wafer inspection method and the inspection apparatus according to the above-described embodiments, and various modifications can be made as necessary.

The configuration of the photodetector is not limited to the one described above, and various configurations can be used depending on the required accuracy, sensitivity, time resolution, and the like. Also, the configuration of the timing synchronization unit can be appropriately changed according to the configuration of the photodetector.

For collecting the scattered light from the abnormal portion of the semiconductor wafer, the light is not limited to the light collecting mirror but may be a light collecting lens, for example. Further, the entire inspection on the semiconductor wafer is not limited to the method in which the wafer mounting table is used as the XY stage as described above. For example, the entire inspection may be performed by scanning the semiconductor wafer with pulsed light. good.

Further, in the above-described inspection method / inspection apparatus, a single pulse light is emitted on the irradiation light path and the detection light path, or on the light path combining the irradiation light path and the reflection light path, or on the range desired by the photodetector. Although the timing and the optical path length are set and controlled so as to exist, a configuration in which a plurality of pulsed lights are simultaneously present depending on the intensity of noise light in each device and the required S / N ratio may be adopted. Alternatively, various configurations are possible, such as providing an aperture at an appropriate position on the irradiation optical path, and using an optical path portion after the aperture as an irradiation optical path for reducing and controlling noise light.

The inspection object is not limited to a semiconductor wafer, and the surface inspection method and inspection apparatus according to the present invention can be similarly applied to a surface inspection of a mask for manufacturing a semiconductor device.

[0090]

As described above in detail, the surface inspection method and the inspection apparatus according to the present invention have the following effects. In other words, in a configuration that detects an abnormal part on the surface of an inspection object such as a semiconductor wafer by detecting scattering of irradiation light, the irradiation light is pulsed, and the timing of its detection operation is set as a photodetector that detects scattered light. And a device having a detection gate function for controlling the time width is used. By performing scattered light detection by operating the irradiation timing and the detection timing by synchronizing with the timing synchronizing means, unnecessary noise light due to scattering of irradiation light or the like on the optical path is detected by the photodetector. It is possible to suppress the detection as the background light and greatly improve the S / N ratio of the detection.

As a result, abnormal spots such as finer dust and scratches generated on the surface of the inspection object can be detected with high efficiency, and the inspection time required for the detection can be shortened. As a result, the inspection apparatus and the inspection process are also simplified. Therefore, for example, in the inspection of a semiconductor wafer or the like, even if the processing dimensions of the semiconductor are further miniaturized in the future, it is possible to inspect and detect an abnormal portion in a sufficient range.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a first embodiment of a semiconductor wafer inspection apparatus according to the present invention.

FIG. 2 is a schematic diagram for explaining the operation and the like of the semiconductor wafer inspection apparatus shown in FIG.

FIG. 3 is a configuration diagram for explaining a detection gate using a streak tube.

FIG. 4 is a configuration diagram schematically showing a second embodiment of the semiconductor wafer inspection apparatus according to the present invention.

FIG. 5 is a configuration diagram schematically showing a third embodiment of the semiconductor wafer inspection apparatus according to the present invention.

FIG. 6 is a configuration diagram schematically showing a fourth embodiment of the semiconductor wafer inspection apparatus according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor wafer, 10 ... Wafer mounting table, 2 ... Pulse laser, 21 ... Reflection mirror, 22 ... Half mirror, 3 ... Photodetector, 30 ... Condensing mirror, 31 ... Streak tube, 32
... CCD, 33 ... Image intensifier, 34 ...
CCD, 35 photomultiplier tube, 4 timing synchronization unit,
Reference numeral 40: branch light detector, 41: timing adjustment unit, 42:
Sweep control units, 43, 44: voltage control unit, 5: optical trap, 6: control unit, 7: display unit.

Continued on the front page F-term (reference) 2F065 AA49 BB01 CC19 DD04 DD06 DD12 FF44 FF67 GG04 GG08 HH12 HH16 JJ01 JJ09 JJ15 JJ26 LL00 LL12 LL19 MM02 MM28 NN02 PP12 QQ28 QQ47 2G051 AA51 BB01 CA07 CB02

Claims (18)

[Claims] 1. A surface inspection method for detecting an abnormal portion on a surface of an inspection object, comprising: a light irradiation step of irradiating a predetermined inspection position on the surface with irradiation light as irradiation light; Detecting a scattered light generated by being scattered by the abnormal portion on the surface by a predetermined detecting means, wherein the light detecting step comprises irradiating the detecting means with the irradiating light. Using a detection gate synchronized to
In the normal state, the detection gate is turned off to suppress the detection of noise light serving as the background light of the scattered light detection, and the predetermined timing and time width in accordance with the timing at which the scattered light arrives at the detection unit are used. A surface inspection method, wherein the detection gate is turned on to detect the scattered light. 2. An irradiation light path which is a light guide path of the irradiation light;
The number of the irradiating light or the pulsed light as the scattered light existing in a range that can be desired by the detecting means in the entire optical path including the detection light path as the light guide path of the scattered light is always 1 at an arbitrary timing. The surface inspection method according to claim 1, wherein the number is equal to or less than the number. 3. An irradiation light path which is a light guide path of the irradiation light;
The irradiation light or the pulsed light, which is the reflected light, exists in a range that the detection unit can expect in a total optical path including a reflected light path that is a light guide path of the reflected light reflected by the surface. 3. The surface inspection method according to claim 1, wherein the number is always one or less at an arbitrary timing. 4. The surface inspection method according to claim 2, wherein the number of the pulse lights existing on the entire optical path is always one or less at an arbitrary timing. 5. A surface inspection apparatus for detecting an abnormal portion on a surface of an inspection object, comprising: a pulse light source that emits pulse light and irradiates a predetermined inspection position on the surface as irradiation light; A photodetector configured to detect scattered light generated by the irradiation light being scattered by the abnormal portion on the surface, and to control the timing and time width of the light detection by a detection gate; and the pulse light source. And timing synchronization means for controlling the timing of detecting the scattered light by the photodetector, wherein the timing synchronization means sets the detection gate to the irradiation timing of the irradiation light. In the normal state, the detection gate is turned off to suppress detection of noise light serving as background light of the scattered light detection. , O the detection gate by combined predetermined timing and duration to the arrival timing to the photodetector of the scattered light
As N, the pulse light source and the photodetector are controlled so that the scattered light is detected. 6. The pulse light source emits the pulse light at a predetermined repetition frequency, and the irradiation light path of the irradiation light from the pulse light source to the inspection position on the surface and the light from the inspection position on the surface. The optical path length of the range that the photodetector can hope for among all the optical paths including the detection optical path of the scattered light up to the detector is set to be shorter than the distance that light travels during the time of one cycle of the repetition frequency. The surface inspection apparatus according to claim 5, wherein 7. The pulse light source further emits the pulse light at a predetermined repetition frequency, and further includes an optical terminal portion that serves as an optical path terminal of the reflected light of the irradiation light reflected by the surface. The photodetector may be desired among all optical paths that combine an irradiation optical path of the irradiation light to the inspection position on the surface and a reflection optical path of the reflected light from the inspection position on the surface to the optical terminal. The surface inspection apparatus according to claim 5, wherein an optical path length of the range is set shorter than a distance that light travels during one cycle of the repetition frequency. 8. The surface inspection apparatus according to claim 6, wherein an optical path length of the entire optical path is set to be shorter than a distance traveled by light during one cycle of the repetition frequency. 9. The photodetector according to claim 1, wherein the photodetector is configured to have a streak tube for performing detection control by the detection gate by a predetermined gate operation or gate structure and generating a detection image from the scattered light. Claims 5-8
The surface inspection device according to any one of claims 1 to 7. 10. The photodetector is configured to include an image intensifier that performs detection control by the detection gate by a predetermined gate operation and generates a detection image from the scattered light. Claims 5 to 8
The surface inspection device according to any one of claims 1 to 7. 11. The surface inspection apparatus according to claim 9, wherein the photodetector further includes a CCD that captures the detected image. 12. The surface inspection apparatus according to claim 9, wherein the photodetector further includes a photomultiplier tube for detecting the detection image. 13. The photodetector according to claim 1, further comprising a photomultiplier tube for detecting the scattered light by performing detection control by the detection gate by a predetermined gate operation. Item 9. The surface inspection device according to any one of items 5 to 8. 14. A method for mounting the inspection object,
The apparatus according to claim 5, further comprising a mounting table for performing inspection on the entire surface of the inspection object by driving the inspection object in a horizontal direction to move the inspection object.
14. The surface inspection apparatus according to claim 13. 15. The surface inspection apparatus according to claim 14, wherein the mounting table is driven to move the inspection target by a distance shorter than a spot diameter of the irradiation light. 16. The surface according to claim 5, wherein the entire surface of the inspection object is inspected by scanning the surface of the inspection object with the irradiation light. Inspection equipment. 17. A control unit for controlling the entire apparatus including the pulse light source, the photodetector, and the timing synchronization unit, and for obtaining or analyzing detection data by the photodetector. Claims 5-1
7. The surface inspection apparatus according to claim 6. 18. The surface inspection apparatus according to claim 17, further comprising display means connected to said control means for displaying operation information on each part of the apparatus or inspection information based on a detection result.