JPS61221716A - Automatic focusing unit for optical inspector using microscope - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application] The present invention generally relates to a device for automatically adjusting the focus of an objective lens used for inspecting an object, and more specifically relates to a device for automatically adjusting the focus of an objective lens used for inspecting an object, and more specifically, it relates to a device for automatically adjusting the focus of an objective lens used for inspecting an object. , utilizes a multi-aperture projection reticle and a pair of multi-aperture return masks, as well as a physical connection between the microscope objective and the reticle or object to move the microscope into a position of focus relative to the object to be inspected. The present invention relates to an electro-optical device that utilizes a corresponding detector to generate a control signal that is used to vary the distance.

[Prior art]

In automatic inspection equipment for objects such as photomasks, it is important to include means for automatically focusing the lens used for inspection work. One takes advantage of the fact that the magnification of a reticle viewed through a lens system is a function of the distance of the reticle from the image plane of that lens.

In that device, as the reticle moves away from the lens and away from the lens' ideal focus position,
A point within the periphery of the field moves inward toward the optical axis of the lens, and similarly, as an object moves toward the lens, a point within the periphery of the field moves outward away from its taper. Thus, by focusing a narrow beam of light on a point within the periphery of the field of view and then detecting the position of that point relative to a known position, the distance between the objective and the object to be examined can be determined. The device works well if the surface of the object being inspected is generally smooth, but it is not acceptable in the case of multi-level surfaces of the type present in silicon wafers on which integrated circuits etc. are formed. Accuracy cannot be obtained.

An automatic lens focusing apparatus configured for inspecting semiconductor wafers and the like is disclosed in U.S. Patent Application No. 582,584, filed February 22, 1984. The invention disclosed in that U.S. patent application is protected by the applicant of the present application, and the U.S. patent application upon which this application claims priority is a continuation-in-part of the above-mentioned U.S. patent application.

The object of the present invention is to obtain an improved autofocusing device.

An object of the present invention is to provide the above-mentioned method capable of focusing with high precision on a target such as a patterned silicon wafer that has large local surface irregularities and fluctuates in reflectance. The goal is to obtain a variety of equipment.

In summary, a preferred embodiment of the present invention includes a light source, a dual channel fiber optic bundle, a means for intermittent light into the channels, and projection of alternating images onto a reticle and an object to be inspected. an associated optical device for examining the return mask and alternating reticle images, and an associated detector for examining the return mask and alternating reticle images, and for driving the microscope in response to the output of this detector to focus the microscope of the device. and a control circuit that operates. This preferred embodiment also includes a flipping pupil to receive a specific objective of one microscope.

A major advantage of the present invention is that it provides a device that can focus on a patterned silicon wafer with many level changes and large contrast variations. This advantage is obtained because both channels return the same image when both channels are in focus. When the channels are subtracted from each other, the effects of the wafer pattern are eliminated. A particular objective of the microscope is thus focused on the local average roughness of the surface area being examined.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

First, refer to FIG. A microscope turret, indicated generally at 10, is held by a turret mounting and positioning assembly 12. This turret mounting and positioning assembly 1
2 is as disclosed in the aforementioned pending US patent application for positioning a selected objective lens from among the microscope objectives over the wafer W to be inspected. The wafer W is supported by a movable table indicated by reference numeral 13 in the cutout portion. Turret mounting and positioning assembly 12 includes a turret drive and positioning mechanism, indicated generally at 14, and a microscope imaging lens system, indicated generally at 16. The optical axis 18 of this device includes one of the objective lenses 20 of the microscope, the imaging lens 16, the field lens 22, the 148IIn lens 24, the gyroic beam splitter 2B, the 300an lens 28, and the pentaprism 30. , and the input lens 32 of the television camera 34. It should be noted that the light is collimated between lenses 24 and 28. The operation of television camera 24 and pentaprism 30 is also described in the aforementioned US patent application. However, it will be appreciated that the present invention can be applied to any optical device that requires automatic focusing of a microscope.
A controller 36 responsive to the signals generated by 8 provides drive signals to turret drive and positioning mechanism 14 .

The autofocus optical system, indicated generally by the reference numeral 40, includes means for forming a first optical path or axis 42. As shown in FIG. The first optical path 42 includes a quartz halogen lamp 44 and a spherical mirror 4.
Starting from 6, the condenser lens 50 and the hot mirror 52
pass through. First optical path 42 is split through mirror 52 into a pair of initially separated parallel optical paths or channels by an aperture in chopper wheel 54 . The channels are formed by light 7-aipa bundles 56 (Channel Person) and 58 (Channel B). Optical fiber bundle 56.58
The light emitted from the end of the pupil is the flippin.
g pupil) 60, red filter 62, and 50
nn pupil lens 64 and multiple aperture projection reticle 66
Pass through. The first optical path 42 then includes a 5% beam splitter 68, a 5% beam splitter 70, and an imaging lens 72.
and then enters the optical path or optical axis 18 of the device at the dichroic beam splitter 26.

A portion of the light passing through the reticle 66 is bent by a beam splitter 68 into a second optical path or optical axis 73 through a detector imaging lens 74 and a reflector 76 to a forward photodetector 78. Proceed along.

Returning from the wafer W, the reflected light along the optical path 42 is bent by a beam splitter 70 and passed through another 50% beam splitter 80, a first return mask 88, a detector lens 90, S-CURVE (S-Curve) detector 92
along a third optical path or optical axis 79 that includes: The light returning along this third optical axis T9 is bent by the beam splitter 80 and travels along the fourth optical path, ie, the optical axis 81, including the second return mask 82 and the detector lens 84. , an optical fiber bundle 56 for transmitting light to a 0 channel A selection detector 96 which is incident on a SUM detector 86.
Note that part of is split at 94. The outputs of detectors 78, 86, 92.96 are all input to preamplifier 38.

As will be explained further below, overall, the autofocus device f! ! , 40 alternately project a pair of red light images of a projection reticle 66 offset in the axial direction onto the wafer W to be inspected. These axially offset images are passed back through the device along optical axes T9 and 81 and focused by a slotted mask onto a photodetector. The position of the slotted image relative to the associated mask will then indicate the state of focus of the microscope.

As mentioned above, this autofocus device utilizes a 100W quartz halogen lamp 44 as a light source.

The light from this light source is collected by a spherical mirror 46, and is then transferred to an optical fiber bundle 56.5 by a mirror 52 and a chopper ring 54.
8 (FIG. 2). The exit ends 57, 59 of the optical fiber bundle are placed at the conjugate image (pupil image) of the rear aperture of the microscope objective. This conjugate image is created by placing the exit end of the optical fiber bundle at one focal point of the pupil lens 64 with a focal length of 50 nn so that the light emitted from the optical fiber bundle passes through the pupil lens 64 and forms a plane. , imaged 0. The light then passes through the projection reticle 66, which is placed at the other focal point of the pupil lens. This reticle 66 is also placed at one focal point of a 100Iff11 autofocus imaging lens 78. The autofocus imaging lens 78 collimates the light passing through the reticle. The collimated light, containing only wavelengths longer than 650 nm as a result of passing through the red filter 62, enters the microscope apparatus through a dichroic mirror 27 forming part of the beam splitter mount 26. 27 reflects light with a wavelength longer than 650 nm and transmits light with a shorter wavelength. Reticle 66
The light that has passed through the microscope is parallel when it enters the optical path inside the microscope, so 148I! In the parallel light region between the llTl microscope lens 24 and the 300-dish microscope imaging lens 28, a reticle image is focused onto the wafer W when the microscope is in focus.

As best shown in FIG. 3, the exit ends 57, 59 of the optical fiber bundles 56, 58 are covered by relatively large fixed apertures 61.

The aperture 61 is 5x, 10x, 20x and 5x.
The conjugate image of the rear aperture of the 0x objective lens is also slightly smaller. The rear aperture of the 100x objective is much smaller than the others, so when the 100x objective is used, the small aperture 6
3 is placed above the larger aperture. The dimensions of this aperture are slightly smaller than the conjugate image of the rear aperture of the 100x objective. The assembly in which the smaller aperture is flipped into the optical path and pushed out of the optical path is called a "flip pupil".

In this embodiment, the chopper wheel 54 is placed directly in front of the optical fiber bundle and has two sets of apertures 54a.

54b successively alternately uncover each optical fiber channel (see also FIG. 2). The chopper wheel 54 has 18
When rotated at 00 RPM, light passing through the aperture moves from "channel to channel" at a rate of 1600 Hz.
It is formed so that it can be switched to. Furthermore, only one channel is illuminated at any given time. any 1
At one time, only the top or bottom half of the rear aperture of any objective will be illuminated. To that end, as the objective lens of the microscope is moved up or down relative to the wafer W, i.e. as the objective lens is moved in or out of its focus, the projection reticle associated with each optical fiber channel is The return image of 66 will be moved down or up. In other words,
When the channel A image moves up, the channel B image moves down, and when the channel A image moves down, the channel B image moves up.

As mentioned above, 50% of the autofocus red light returned from wafer W is split from the main beam by beam splitter TO, which is located between imaging lens 72 and projection reticle 66.

The light is then split into two equal beams by a beam splitter 80, each of which alternately forms an image of the reticle on a return mask 82.88. It will be seen that as each return image moves laterally (relative to the longitudinal axis of each aperture) on the respective return mask 82,88. The light passing through each return mask is focused onto detector lenses 84, 90 and silicon photodetectors 86, 92, respectively.

Next, refer to FIG. In this figure, the preferred embodiment of the projection reticle is shown with five transparent bars 61 within the opaque field of view.
It is shown that it is composed of. Images of those five bars are focused on an area on the wafer. The height of the area is equal to the width of the field of view of the television camera 34, and the width of the area is three times the length. However, it should be noted that the shape and dimensions of the aperture are not limited thereto.

Each return mask 82,88 (FIG. 5) consists of a similar play of transparent bars 87 on an opaque background. When the microscope is focused, the reticle images from both channels coincide, as shown at 89 in FIG.
5-CURVE Aligned to return mask. When the objective lens moves upward from its focal position, channel A
The reticle image associated with channel B moves up (the reticle image from channel B moves down), thus increasing the light from channel A (and B) that is incident on the 5-CURVE detector 92. As the microscope objective moves down, the image in channel A moves down (and the image in channel B moves up), reducing the light incident on the detector.

5-CURVE detector 92, as detailed below.
The current output of is sent through a current-voltage amplifier. Therefore, the voltage output of the 5-CURVE detector/amplifier exhibits approximately the variation shown in FIG. 6 with the position of the focus. When the objective lens is almost in focus, the B channel image moves in the opposite direction to the A channel image, so 5-CURV
E is reversed for channel B signals.

When the outputs of the detector/amplifiers are multiplexed into the chopper wheel 54 and one voltage is subtracted from the other, the result is a curve similar to that shown in FIG. Due to the background light level, which is constant in one channel but different between channels, the curve does not pass through zero when in focus. This focus bias is later subtracted by the autofocus controller. Note that when the microscope is in focus, the returned p-images of both channels are the same, so the returned light is independent of the pattern on the wafer. This means that the reticle image returning from the wafer is
This is extremely important because it includes not only the reticle pattern but also the wafer pattern.

The second return mask is a SUM mask, identical to the S-CURVE mask, except that the projected bar is aligned with the corresponding return projection reticle image such that the projected bar is centered in the SUM return border mask 82 bright slot 87. It is. Therefore, the light in both channels behaves the same. The lights are added together to form the signal shown in FIG.

The intensity of the projected light of automatic focus is S-CURVE and S
In order not to affect the level of the UM signal and to eliminate the effects of differences in the efficiency of the optical fibers of channels A and B, the device includes a forward detector 78. As mentioned earlier, 4% of the light passing through the projection reticle 66 is split from the main projection beam by the plate beam splitter (68) and focused by the third detector lens γ4 onto the detector T8. . The output of detector T8 is converted to a voltage and split into the voltage outputs of the 5-CURVE and SUM detector/amplifiers. The signal from the front detector T8 is also used to synchronize the multiplexer signals in the autofocus preamplifier.

A fourth detector 96 is included to facilitate device synchronization. Several optical fibers 94 are separated from channel A fiber optic bundle 56 and used for direct input to channel selection detector 96.

Forward detector T8 records correctly when any channel is on, but channel selection detector 96 records when only channel A is on. The voltage output of the autofocus preamplifier is summarized as: 0 There is a certain background associated with each Vaa, V+sb, Vsuma, Vsumb. They can be represented by the following definitions.

Vi = Vi'+VW, i = Sa, Sb,
suma, number where viI is the portion of Vt that depends on the focal position and vIN is the associated background signal due to scattered light and curvature from the lens surface that is independent of the focal length of the objective.

(vi' and viI are of the same size) Also, F
Let a and Fb represent the forward detector signals for channels A and B, respectively, then the 5-CURYE signal is given by and the SUM signal is given by .

As explained in the specification of the pending U.S. patent application, when the device is in macro mode, there is no wafer under the microscope (5-CURVE detector and 80M).
All that is read from the detector is the background signal. This signal is a function of the magnification of the objective lens and is otherwise constant.

and , are obtained. Substituting equation (4) into equation (2), and substituting equation (5) into equation (31), we get (MACRO) and S
Record UM (MACRO) and subtract them from the 5-CURVE and SUM outputs when the instrument is in focus. This gives us and .

To compensate the signal for wafer reflectance variations and background signals, the final R return signal is obtained by dividing equation (8) by equation (9). That is, Fa
Fb Fa Fb Next, refer to FIG. This figure shows autofocus preamplifier 3.
8 is a functional block diagram of FIG. This autofocus preamplifier has the outputs of a focus (S-CURVE) detector 92 and an 80M detector 86 and uses their signals to derive a difference (S-CURV
E) Output and SUM (reflectance) output from output terminal 100,1
02 and provide their outputs to autofocus controller 36 (FIG. 1). Processing of the two input signals to the autofocus controller is performed in substantially the same manner.

The output of the focus detector 92 consists of alternating current pulses corresponding to each of the two interrupted pupils separated by a gap such that the two interrupted pupils are "off";
It is input to a chopper stabilizing amplifier 104 configured as a voltage converter. As a result, a voltage waveform W1 is generated at the point shown. (See also Figure 10).

The basic function of an autofocus preamplifier is to determine the difference between two time-multiplexed values of its signal. However, the strength of the two eyes and the eyes are not completely balanced, so
The focus signal must first be normalized with respect to the intensity of the forward traveling light. This is done using the output of the front sensor TB. The forward sensor measures a small fraction of the light traveling forward. As shown in FIG.
The output of 8 is input to the current-voltage converter 106 and the waveform W
The focus signal W1 is then divided by the signal W3 to normalize the focus return signal to the forward pupil intensity.

The division of signal W1 by signal W3 is performed using analog divider 1 (1
8) to prevent the device from saturating when both pupils are off (divisor input equal to zero). A hold function 110 is added to the divisor input to hold the previous channel value during its off period. This generates a normalized focus signal W5. (Figure 10)
In addition to balancing the two channels, the normalization also makes the device independent of the brightness of the focal illuminator.

A difference signal is calculated for each pair of sensor inputs.

The fourth pupil is used to instruct which pupil operates at any given time.
sensor 96 (A-selection) is used.

In the round that generates waveform W4, that sensor is buffered like any other sensor. The waveform W4 is the forward signal W3
It is also used to control the timing logic for sum and difference circuits. The normalized focus signal is provided to a balanced modulator 112. The balanced modulator has a gain equal to minus one for the first channel of the pair of channels. Then output W7 is integrator 1
14, it is integrated over a time determined by timing logic 116 and the result is temporarily held. For the second channel of the pair, the modulator gain is switched to +1 and signal W7 is re-integrated for the same integration time as for the first channel. Therefore, the output of the integrator rises gradually for the first channel and falls gradually for the second channel.

The net output of the integrator after this processing represents the difference between the two time multiplexed signals. That value is sampled and held by a sample and hold circuit (switch 118 and capacitor 120) and then amplified by amplifier 122 to produce an S-CURVE (difference) output at terminal 100. Integrator 114 is then reset and the cycle repeats. This integration/sampling/resetting process minimizes the effects of sensor noise and preamplifier noise.

The SUM output produced at terminal 102 is such that the normalized signal is integrated in the same direction for both channels to produce a signal that in this case represents the sum of the individual time-multiplexed signals. is generated in a similar manner to the 5-CURVE (difference) output, except that no balanced modulator is required.

Reference is now made to FIG. 11, which is a block diagram showing the main components of autofocus controller 36. It can be seen that the autofocus controller 36 processes the 8-CURVE and SUM signals generated by the preamplifier 38 and the encoded position signal to drive the objective lens mount to the focus position. Dew. Operation of autofocus controller 36 is initiated by instructions sent via a serial data link from a main computer (not shown). This automatic focus controller
In addition to the functional components shown in FIG. 1, a one-chip microcomputer/microcontroller 120 is included.

Rotation of the shaft of the DC motor used to drive the microscope positioning mechanism 14 is monitored by an incremental angle encoder (not shown). This incremental angle encoder provides a biphasic combined pulse to the encoder logic 122 of the autofocus controller. The logic then provides a 16-bit absolute position count to microcomputer 120 via data bus 124. 2000 counts corresponds to one rotation of the motor shaft. Rotation of that axis is translated into a 20 micron movement of the objective lens mount via a micrometer drive mechanism and lever arm included in device 12 (FIG. 1).

The SUM signal is applied to input terminal 126 as a differential signal. The differential signal is converted to single-ended form by amplifier 128 and then converted to an 8-bit digital signal by analog-to-digital converter 130.

The 5-CURVE signal at input terminal 132 is also connected to amplifier 1.
34, it can be changed from digital to single-ended format. The signal is then provided to an analog divider 136 in which the 5-CURVE
The offset voltage is subtracted from it and the difference is divided by the sum normalized voltage. Thereafter, in this way the conditioned JS-CURYE signal is
A digital converter 138 converts it into a 910-bit digital signal.

As shown, the 5-CURVE offset signal and the SUM
The normalized signals are set by the microcomputer 120 and converted to analog form by digital-to-analog converters 140, 142, respectively. The SUM and 5-CURVE signals generated at the output terminals of analog-to-digital converters 130 and 138, respectively, are read by microcomputer 120.

Autofocus controller 36 generates an analog motor drive signal at output terminal 146 via an 8-pin D/A converter 144 . This signal generated is applied to another power amplifier and then to a DC motor that drives the objective lens mount 12 via a mechanical linkage as previously described. The motor movement is fed back as encoder changes and/or changes in the 5-CURVE signal so that the microcomputer can perform closed loop servo control.

Reference is now made to FIGS. 12 and 13. It will be seen that the autofocus device of the present invention employs two types of control loops. 0 optical limit sensor indicating position control loop (not shown)
monitors the upper and lower limits of lever arm movement within the autofocus device 12 and the encoder count is initialized with reference to the upper limits. In order to stabilize the control loop, the microcomputer configures a second type of digital filter using software. FIG. 13 shows a 5-CURVE control loop. This servo loop can only operate in the linear region of 5-CURVE. The specimen curve for each objective shows that the slope of the curve becomes steeper with the objective magnification. The amplitude of the curve is also proportional to the reflectance of the Ueno 1 surface. Because of these factors, if no compensation is performed, the open loop gain of the focus servo will be changed. Therefore, the microcomputer sets the gain of the software digital filter. This compensates for changes in the slope of the curve due to the magnification of the objective lens. The change in reflectance is normalized by dividing the incoming 5-CURVE by the SUM normalized voltage. Since the signal obtained by SUM is also proportional to the reflectance of the wafer, the output from the analog divider is the reflectance normalized 5-CURVE signal.

The resulting input to the S-CURVE analog-to-digital converter is . Their "macro" values are first subtracted.

This is because these "macro" values are offsets resulting from optical ghosts that are not related to the signal reflected from the wafer.

This autofocus servo loop, in contrast to the position (encoder) loop, contains additional elements, and therefore, for stability, the second digital filter for compensation has poles and zeros placed differently. have An advantage of software digital filters is that the coefficients can be easily changed to optimize the configuration of the device.

In operation, automatic focus controller 36 responds to commands from the main computer to locate and lock the objective lens mount to a desired (target) position (
For example, moving the objective lens to a safe retraction height where it does not disturb the wafer, or performing other operations required to make this autofocus device function with the rest of the mechanism. Although it is simple, it is necessary to describe the J routine that searches for the focal point and the routine that maintains the focal position.

All functions of the autofocus controller occur within a repeating time cycle of about 700 microseconds. Therefore, for each cycle the autofocus controller connects the SUM-A/D converter and the SUM-A/D converter.
-CURVE-A/D converter and position.

Sample the encoder and input command line. The autofocus controller also outputs the drive signal for the DC position control motor, and the zero timer cycle that updates the output status line has separate time sampling periods for the digital filters used in the position and focus loops.

The operation of the focus finding routine is shown in FIG.

In FIG. 14, the vertical axis represents the vertical position of the objective lens mount. Also shown is the S-CURVE signal. The horizontal time axis represents the amplitude and direction of the drive voltage. The focus search begins from a retracted position above the start of the S-CURVE. Then, upon receiving a command that allows movement of the objective lens mount to seek the zero focus drawn relative to their axes, the automatic focus controller applies the highest drive voltage to move the objective lens to S-CU.
When the autofocus controller detects the zero crossing of 5-CURVE, the autofocus controller records the corresponding encoder position as the desired focus position. At the same time, first Apply the highest drive voltage in the direction of increase to stop the objective lens mount, then reverse the movement of the objective lens mount. At this point the automatic focus controller records the stop position and the distance between that stop position and the focus The automatic focus controller then applies a full drive voltage to drive the objective lens mount to the target position, and finally applies a downward drive voltage to bring it to a final stop in focus.At this point the automatic The focus controller exits the open-loop control mode and closes the focus loop to servo control the focus position.In practice, it takes into account factors such as elastic stretching of mechanical parts and additional zero-crossings of the S-CURVE. To correct, the above operation is a little more complicated. When the zero focus loop is closed with the selected filter value, the autofocus device servos at the zero position on the S-CURVE. However, the autofocus device ( (by infrared)
There is a definite misalignment between the measured optimal focus position and the focus position monitored (in visible light) by the television camera. This positional shift is called color blurring, and differs depending on the objective lens. The color shift is measured for each objective during initial calibration. Once the focus position is reached, the automatic focus controller moves the objective lens mount to its calibrated color.
To control the height of the objective lens with respect to the focus of the 5-CURVE, another offset may be applied. This is useful when viewing with magnification.

[Brief explanation of drawings]

Fig. 1 is an exploded perspective view showing the automatic focusing device of the present invention;
3 is a diagram detailing the illuminated end of the optical chopper ring and associated fiber optic bundle; FIG. 3 is a diagram detailing the dual aperture pupil arrangement used in the present invention; and FIG. Figure 5 shows the projection reticle image and S-CURVE when the microscope is in focus.
A line diagram showing how the masks are aligned, FIG.
7 and 8 are curves showing the operation of the autofocus device of the present invention, FIG. 9 is a block diagram showing the main functional components of the autofocus preamplifier of the present invention, and FIG. 10 is a curve showing the operation of the autofocus device of the present invention. FIG. 11 is a block diagram showing the main functional parts of the automatic focus controller of the present invention, and FIGS. 12 and 13 are diagrams of signal waveforms at specific points in the block diagram. FIG. 14 is a functional block diagram showing the control loop; FIG. 14 is a diagram showing the focus finding operation of the present invention; 14... Turret drive and positioning mechanism; 26.
68, 70, 80・Φ・・Beam splitter, 34・・・・
Television camera, 38... Autofocus preamplifier, 44
...Light source, 54...Chopper ring, 56.58.
Φ... Optical fiber bundle, 60... Pupil, 66...
Projection reticle, 74...Detector imaging lens, T6@
...Reflector, 78...Front photodetector, 82,88
...Φ return mask, 86@...SUM detector, 92
・---5-CURVE detector, 102--"Chopper stabilization amplifier, 106...Current-power converter, 11
2...Balanced modulator, 114...Integrator, 120
... Microcomputer, 122 ... Encoder logic, 130, 138 ... Φ Analog-digital converter, 140, 142 ... Digital-analog converter. Patent applicant: KLA Instruments Corporation

Claims (20)

[Claims] (1) Optical inspection using a microscope of the type used to inspect objects such as semiconductor wafers, with an optical inspection axis extending between an inspection instrument and an electrically controllable microscope device. In an autofocus device of the apparatus, means for forming a first optical axis having a light source at one end and a first beam splitter positioned along the optical inspection axis at the other end; alternately transmitting spatially separated bursts of light rays from opposite sides of the optical axis of the microscope along said first optical axis to pupil means located at a conjugate image location of the rear aperture of the microscope objective. means disposed along the first optical axis; and reticle means disposed along the first optical axis between the pupil means and the first beam splitter. , reticle means having an aperture means formed therein such that each burst of light from the pupil passes through the reticle means and projects an image of the aperture means onto an object to be examined by the microscopic device; a second beam splitter disposed between the reticle means and the first beam splitter; a third beam splitter; and an electronic controller, wherein the first beam splitter is arranged between the first beam splitter and the first beam splitter. the second beam splitter is operative to direct light from one optical axis into the microscopy device and to return light reflected from the microscopy device along the first optical axis; One end directs the light returned from the object, including the image of the aperture means, into the second
a beam splitter, the other end of which is operative to deflect onto a second optical axis defined by an S-curve photodetector means; a first return mask disposed along the second optical axis, and the third beam splitter is disposed between the second beam splitter and the first return mask along the second optical axis. reflecting a portion of said returning light along a third optical axis having said third beam splitter at one end and Wako detector means at the other end; includes a second return mask disposed between it and said Wako detector means, said electronic controller controlling the output signal generated by said Wako detector means and the output signal generated by said S-curve photodetector means. and generating, in response to the output signal, a drive signal for controlling the positioning of the microscopy device relative to the object being inspected so that the microscopy device focuses on the average local roughness of the surface area being inspected. An automatic focusing device for an optical inspection device using a microscope, characterized in that it operates as follows. (2) The automatic focusing device according to claim 1, wherein the means for alternately sending the light beams includes a light interrupting means and a pair of parallel optical fiber bundles, and an input of the optical fiber bundles. an end located close to the light interrupting means;
an output end of said fiber optic bundle is positioned proximate said pupil means, and said light interruption means is operative to alternately admit light from said light source into each said fiber optic bundle. Focusing device. (3) The automatic focusing device according to claim 2, wherein the light intermittent means includes a rotatable drive wheel, and the drive wheel periodically introduces the light into one of the optical fiber bundles. and a second circular array of apertures radially offset with respect to the first array, the second array having a first circular array of apertures for transmitting light to the first circular array.
an automatic focusing device, characterized in that it operates to periodically introduce the light into the second optical fiber bundle while no light is introduced into the second optical fiber bundle. (4) An automatic focusing device according to claim 1, wherein the pupil aperture is always slightly smaller than the rear aperture of the objective lens of the particular microscope in use;
An autofocus device characterized in that said pupil means includes means for selectively varying the diameter of the pupil aperture. (5) An autofocus device according to claim 4, wherein the changing means includes a first plate having a first pupil aperture of a first diameter and adjacent to the first plate. a second plate selectively positionable in relation to the autofocus device, the second plate having a second pupil aperture having a second diameter shorter than the first diameter. (6) An autofocus device as claimed in claim 1, wherein the aperture means of the reticle means includes at least one elongated aperture, the width of which is the width of the field of view of the optical inspection device. An autofocus device for projecting an image onto an object having a width less than its width, wherein the length of the elongated aperture causes the length of the image to be at least twice the width of the field of view. (7) An autofocus device according to claim 6, characterized in that the aperture means is formed by a plurality of parallel oriented slot-like transparent portions of an opaque device. Device. (8) The automatic focusing device according to claim 6, wherein the first return mask and the second return mask are
An automatic focusing device configured to match an image projected by the reticle means. (9) The automatic focusing device according to claim 1, wherein when the object is in focus, the first return mask detects an equal portion of the image of the aperture means by the S-curve light. an automatic focusing device, characterized in that the automatic focusing device is positioned such that when the object is out of focus, it is positioned so as to cause less than an equal portion of the image of the aperture means to enter the image of the aperture means; (10) An automatic focusing device according to claim 9, which includes the entire image of the aperture means when the object is in focus, and when the object is out of focus, the entire image of the aperture means is included. Autofocus device, characterized in that a second return mask is provided to include less than all the images. (11) The automatic focusing device according to claim 1, wherein the means arranged along the first optical axis comprises:
An automatic focusing device comprising means for restricting light passed through said reticle means to fall within a predetermined wavelength range. (12) The automatic focusing device according to claim 11, wherein the means for sending the light beams alternately includes a light interrupting means and a pair of parallel optical fiber bundles, and the input end of the optical fiber bundles are positioned proximate said optical fiber bundles, and the output ends of said optical fiber bundles are positioned proximate said pupil means, and said light disconnection means directs light from said light source to said respective optical fiber bundles. An automatic focusing device characterized in that it operates in such a way as to alternately focus on each other. (13) An automatic focusing device according to claim 12, wherein the diameter of the pupil aperture is adjusted such that the pupil aperture is always slightly smaller than the rear aperture of a particular objective lens during use of the microscope. An autofocus device characterized in that it includes means for selectively changing. (14) The autofocus device of claim 13, wherein the reticle means includes at least one elongated aperture, the width of the aperture being narrower than the width of the field of view of the optical inspection device. project an image onto an object that has
An autofocus device characterized in that the length of the elongated aperture makes the length of the image location at least twice the width of the field of view. (15) The automatic focusing device according to claim 14, wherein when the object is in focus, the first return mask detects an equal portion of the image of the aperture means by the S-curve light. an automatic focusing device, characterized in that the automatic focusing device is positioned such that when the object is out of focus, it is positioned so as to cause less than an equal portion of the image of the aperture means to enter the image of the aperture means; (16) An automatic focusing device according to claim 15, which captures the entire image of the aperture means when the object is in focus, and captures the entire image of the aperture means when the object is out of focus. The second one to include all fewer statues.
An autofocus device characterized in that it is provided with a return mask. (17) The automatic focusing device according to claim 16, wherein a fourth beam splitter is arranged between the reticle means and the second beam splitter along the first optical axis. further comprising a fourth beam splitter, the fourth beam splitter having at one end a portion of the light passing through the reticle means, and having photodetector means for detecting the forwardly traveling light. reflecting along a fourth optical axis disposed at the other end, said electronic controller detecting a burst of forward light in response to an output signal generated by a photodetector means for detecting said forward traveling light; An automatic focusing device characterized in that it operates to eliminate any effects due to differences in intensity or duration. (18) The automatic focusing device according to claim 15, comprising a fourth photodetector means, the fourth photodetector means being on one side of the first optical axis. An autofocus device operative to generate a synchronization signal for input to said electronic controller in response to light corresponding to a burst of light transmitted to said pupil means. (19) Optical inspection using a microscope of the type used to inspect objects such as semiconductor wafers, with an optical inspection axis extending between an inspection instrument and an electrically controllable microscope device. In an autofocus device of the apparatus, means for forming a first optical axis having a light source at one end and a first beam splitter positioned along the optical inspection axis at the other end; alternately transmitting spatially separated bursts of light rays from opposite sides of the optical axis of the microscope along said first optical axis to pupil means located at a conjugate image location of the rear aperture of the microscope objective. means disposed along the first optical axis; and reticle means disposed along the first optical axis between the pupil means and the first beam splitter. , reticle means having an aperture means formed therein such that each burst of light from the pupil passes through the reticle means and projects an image of the aperture means onto an object to be examined by the microscopic device; a second beam splitter disposed between the reticle means and the first beam splitter; a third beam splitter; and an electronic controller, wherein the first beam splitter is arranged between the first beam splitter and the first beam splitter. the second beam splitter is operative to direct light from one optical axis into the microscopy device and to return light reflected from the microscopy device along the first optical axis; One end directs the light returned from the object, including the image of the aperture means, into the second
a beam splitter, the other end of which is operative to deflect onto a second optical axis defined by an S-curve photodetector means; a first return mask disposed along the second optical axis, and the third beam splitter is disposed between the second beam splitter and the first return mask along the second optical axis. reflecting a portion of said returning light along a third optical axis having said third beam splitter at one end and Wako detector means at the other end; includes a second return mask disposed between it and said Wako detector means, said electronic controller controlling the output signal generated by said Wako detector means and the output signal generated by said S-curve photodetector means. and generating, in response to the output signal, a drive signal for controlling the positioning of the microscopy device relative to the object being inspected so that the microscopy device focuses on the average local roughness of the surface area being inspected. further comprising a fourth beam splitter arranged along the first optical axis between the reticle means and the second beam splitter, the fourth beam splitter operatively disposed between the reticle means and the second beam splitter; reflecting a portion of the light passing through the means along a fourth optical axis having said fourth beam splitter at one end and photodetector means for detecting forwardly traveling light located at the other end; and said electronic controller is responsive to an output signal generated by a photodetector means for detecting said forwardly traveling light to eliminate any effects due to differences in intensity or duration of said bursts of light. An automatic focusing device for an optical inspection device using a microscope, characterized in that it operates to: (20) The automatic focusing device according to claim 19, comprising a fourth photodetector means, the fourth photodetector means being on one side of the first optical axis. An autofocus device operative to generate a synchronization signal for input to said electronic controller in response to light corresponding to a burst of light transmitted to said pupil means.