JPS6211142A - Apparatus for inspecting foreign matter - Google Patents

Abstract

PURPOSE:To make it possible to rapidly and easily set an optimum inspection condition, by repeating the inspection of foreign matter to the same article to be inspected plural times while changing a condition and storing the inspection data of each time in a memory means. CONSTITUTION:A foreign matter inspection apparatus for a wafer is constituted so that a Z-stage 20 is provided on an X-stage 10 and a wafer 30 as an article to be inspected is mounted thereof to be rotated by a rotary stage 22. Foreign matter 30 is irradiated with S-polarized laser beams 36, 38 and the reflected beams reach a 45 deg. prism 60 through the optical system common to a detection system 50 detecting the foreign matter and a microscope 52 for the visual observation of the wafer, that is, an objective lens 54, a half mirror 56 and a prism 58. The inspection of the foreign matter to the same article to be inspected is repeated plural times while a condition changes and the resulting data of the inspection of the foreign matter at each time is stored in a memory means and the operation mode thereof is preliminarily imparted to the foreign-matter inspection apparatus to automatically obtain the inspection data of the foreign matter under various inspection conditions and an optimum condition is easily judged from the resulting data.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a foreign matter inspection device for inspecting the presence or absence of foreign matter on the surface of an object to be inspected such as an LSI wafer.

[Prior art] As a foreign matter inspection device for LSI wafers, a light beam is irradiated onto the wafer, the reflected light from the wafer is received by a light receiving element and converted into an electrical signal, and the wafer is inspected based on this electrical signal. There is a type that determines the presence or absence of foreign objects.

Conventionally, a photomultiplier has been used as this light receiving element. There is a relationship as shown in FIG. 4 between the output signal level of the photomultiplier and the particle size of the foreign material. A curve S shown in this figure is a sensitivity curve of the photomultiplier, and this sensitivity curve S changes depending on the voltage applied to the photomultiplier. Further, LB indicates the level of background noise. This background noise level is influenced by the state of the wafer, the patterns provided on the wafer, and the like.

As can be easily understood from Fig. 4, if the applied voltage of the photomultiplier is increased and the sensitivity curve S rises, the detection ability for minute foreign objects will increase to 1.0, but the sensitivity curve will become saturated. In addition, the maximum foreign particle diameter that can be detected by +1J becomes smaller (the dynamic range becomes narrower). On the other hand, if the applied voltage of the photomultiplier is lowered to make the γ-L gradient of the sensitivity curve S gentler, it is possible to detect even large foreign objects (the dynamic range is widened), but the ability to detect minute foreign objects is descend.

In the case of patterned wafers, the background noise is high due to the influence of the pattern, so only foreign particles of, for example, 3 μm or larger can be detected, so the sensitivity is reduced to F.
It is common to widen the dynamic range. On the other hand,
In the case of a mirror-finished wafer or a wafer with a blank film, the level of background noise is low, so it is common to reduce the sensitivity by -L to increase the detection ability of minute foreign matter by -L.

There is also a correlation between the background noise level and the irradiation angle of the light beam on the wafer, and the optimal irradiation angle differs depending on the type of wafer to be inspected.

Therefore, foreign matter inspection apparatuses have been known in which inspection conditions such as the voltage applied to a photomultiplier and the irradiation angle of a light beam can be changed.

[Problems to be Solved] In order to set such optimal conditions, it is necessary to obtain information for that purpose. However, the conventional foreign object inspection apparatus does not have a special function to assist in collecting this information, and therefore, it is inconvenient that it takes time and effort to collect this information.

In addition, if the conditions are found to be inappropriate after inspection under certain conditions, it is necessary to reset the conditions, set the wafer again, and perform the inspection again, which takes a lot of time and effort. There was a problem that there was a significant increase in

[Purpose of the Invention] This invention was made in view of the problems of the prior art described above, and it is possible to quickly obtain information for setting the optimum conditions for inspection, and also to be able to quickly obtain information for setting the optimum conditions for inspection. Another object of the present invention is to provide a foreign matter inspection device that can efficiently obtain necessary foreign matter inspection results.

In order to achieve the objective 1, the foreign matter inspection device according to the present invention repeats the foreign matter inspection on the same inspection object multiple times under different conditions, and detects foreign matter at each time. It has an operating mode in which test result data is stored in a storage stage.

[Effects] This operation mode automatically obtains foreign substance inspection result data under various inspection conditions, so the optimum conditions can be easily determined from the result data and the optimum inspection conditions can be set quickly and easily. can.

In addition, if the optimal conditions are unclear, it is possible to select and adopt the foreign material inspection result data under the optimal conditions from among the foreign material inspection result data obtained under various conditions in such operation modes. The time and labor required for testing can be significantly reduced compared to testing by resetting the conditions with manual intervention.

[Embodiment] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing a simplified structure of the optical system and other components of the wafer foreign matter inspection apparatus according to the present invention. In this figure, 10 is an X stage supported by a base 12 so as to be slidable in the X direction.

This X stage 10 (this is screwed with a screw 16 directly connected to the rotating shaft of a stepping motor 14, and by operating the stepping motor 14, the X stage 10 can be moved forward and backward in the X direction.18 is X
This is a linear encoder that generates a code signal corresponding to the position X of the stage 10 in the X direction.

An X stage 20 is attached to the X stage 10 so as to be movable in the Z direction. The driving means is omitted in the figure. Furthermore, a rotation stage 22 on which a wafer 30 as an object to be inspected is placed is supported by the X stage 20 in one rotational capacity. Here, as the wafer 30, a wafer with a blank film, a mirror wafer, or a wafer with a pattern can be set and inspected.

This rotation stage 22 is connected to a stepping motor 24, and is rotated by operating the stepping motor 24. This stepping motor 24 has
A rotary encoder that outputs a code signal corresponding to the rotational direction position 0 of the rotary stage 22 is built-in.

Note that the wafer 30 is positioned and fixed on the rotation stage 22 by negative pressure suction, but means for this purpose are omitted in the figure.

This wafer foreign matter inspection device automatically inspects foreign matter on a wafer 30 using polarized laser light, and the upper surface (inspected surface) of the wafer 30 is irradiated with S-polarized laser light. For that purpose, S-polarized laser oscillation 79136.3
8 is provided. Each S polarization laser oscillator 36.38
is a semiconductor laser oscillator that generates S-polarized laser light of a certain wavelength, for example, a wavelength of 8300 angstroms.

The S-polarized laser light is irradiated onto the wafer 30 from the Y direction at an irradiation angle φ of approximately 2 degrees. Since the irradiation angle is thus small, when a beam of S-polarized laser light having a circular cross section is irradiated, the spot on the wafer is elongated, making it impossible to obtain an irradiation density of 1 minute. Therefore, a cylindrical lens 44, 46 is arranged in front of the S-polarized laser oscillator 36° 38, and the S-polarized laser beam with an approximately circular cross section emitted from the S-polarized laser oscillator 38, 38 is transformed into a flat cross-sectional shape collapsed in the Z direction. The wafer is then irradiated with a focused beam.

Here, in the case of a wafer with a blank film without a pattern (or a mirror-finished wafer), if there is no foreign matter in the irradiation spot, the S-polarized laser light will be almost specularly reflected and will not be reflected in the Z direction. If there is, the light will be diffusely reflected and reflected in two directions.

On the other hand, in the case of a patterned wafer, the reflected laser beam of the S-polarized laser beam irradiated onto the wafer is also reflected in the Z direction if a pattern exists within the irradiation spot.
Since the surface of the pattern is microscopically (k-smooth), the reflected laser light is almost only the S-polarized component.
The surface of a foreign object generally has minute irregularities, so if a foreign object is present within the irradiation spot, the irradiated S-polarized laser light will be scattered and the polarization direction will change, and the reflected laser light will contain components other than the S-polarized light component. The light contains a considerable amount of P-polarized light component.

In response to this phenomenon [1], in the case of patterned wafers, this wafer foreign particle inspection device detects foreign particles based on the level of the P-polarized light component contained in the laser beam reflected from the wafer in the Z direction. Detects the presence or absence of foreign objects and the size of foreign objects.

On the other hand, in the case of a wafer with a blank film (including mirror-finished wafers), in order to increase detection sensitivity, the presence or absence and size of foreign particles can be determined based on the levels of the S-polarized reflected laser beam and the P-polarized reflected laser beam in the Z direction. Detect.

Refer to FIG. The reflected laser light from the wafer enters an optical system common to a detection system 50 for detecting foreign matter according to the above principle and a microscope 52 for visual observation of the wafer. That is, the reflected laser beam passes through the objective lens 54, the half mirror 56, and the prism 58.
degree prism 60 is reached.

A lamp 70 is also provided for visual observation. The irJ viewing light emitted from the lamp 70 illuminates the wafer through the half mirror 56 and the objective lens 54. The reflected light also reaches the 45 degree prism 60 similarly to the reflected laser light.

The visible reflected light that has entered the microscope 52 side via the prism 60 is transmitted through a 60 degree prism 62, a field lens 64,
The light passes through the relay lens 66 in order and enters the eyepiece lens 68. Therefore, the wafer 30 can be visually observed through the eyepiece 68 at a sufficiently high magnification. In this case, the range of the S-polarized laser beam spot on the wafer surface is located at the center of the field of view. Also, through the prism 58, the sea urchin/
%30 can also be observed at low magnification.

The reflected laser light that has entered the detection system side via the prism 60 passes through the aperture 4 provided in the slit 72 and is sent to the photomultiplier 90.

Here, if the wafer 30 is a patterned wafer,
Since the S polarization cut filter 86 (polarizing plate) is moved to the position indicated by the symbol 86, the P polarization of the reflected laser beam is
Only the polarized light component is extracted and enters the photomultiplier 90. When the wafer 30 is a wafer with a blank film (or a mirror wafer), the S polarization cut filter 88 is moved to the position shown by the solid line, so that both the S polarization component and the P polarization component of the reflected laser light enter the photomultiplier 90. . As will be described later, based on the level of the output signal (detection signal) of the photomultiplier 90, the presence or absence of a foreign object within the field of view of the aperture 4 of the wafer 1 is determined.
The particle size of the foreign object is determined.

87 is a solenoid for moving the S polarization cut filter 86.

Here, the foreign matter inspection is performed while rotating the wafer and feeding it in the X direction (C\: radial direction) as described above. According to such movement of the wafer 30, as shown in FIG.
A spot 30A of polarized laser light moves spirally from the outside toward the center of the wafer 30. Detection system 50
The microscope 52 is stationary, and the field of view of the aperture 4 is always included within the spot 30A, and moves to follow the spot 30A. That is, the wafer is inspected while being spirally scanned.

Here, the irradiation angle φ will be explained. In conventional wafer particle inspection equipment, when inspecting a wafer whose surface has a blank film without a pattern, such as a photoresist film or an aluminum evaporated film, for particle inspection, the light beam is emitted at a fairly large irradiation angle, for example, 30 degrees. The wafer itself is irradiated.

According to the inventor's research, the background noise of the detection signal in such conventional devices includes not only noise components determined by the state of the wafer surface (the surface of the blank film) (but also noise components related to the internal state of the blank film). It contains a noise component and a noise component related to the state of the wafer base surface under the blank film.Principle 1-1 of using reflected light from the wafer surface 1-1 Completely remove the first noise component is not possible, and its influence is not fatal.However, the latter two noise components are affected by the internal state of the wafer and directly cause 5ti detection, so they should be removed. It is something that should be done.

According to the inventor's research, in the conventional device, because the beam irradiation angle is large, a part of the light beam incident on the wafer surface enters the inside of the blank film, is reflected on the wafer base surface, and the blank film increases by 1 f. It was found that the above-mentioned undesirable noise component was generated due to the noise passing through the wafer surface and entering the charging element.

Therefore, in this embodiment, the irradiation angle of the light beam is selected to be 1.0 min smaller as described above so that the light beam is substantially totally reflected by the wafer, thereby preventing the light beam from penetrating into the wafer. I'm confused.

Next, the signal processing and control system of this wafer foreign matter inspection apparatus will be explained with reference to FIG.

The detection signal output from the photomultiplier 90 is amplified by an amplifier 100 and then sent to the level comparison circuit 1.
It will be man-powered in 02.

Here, there is a relationship as shown in FIG. 4 between the particle size of the foreign matter on the wafer 1 and the level of the detection signal. however,
Naturally, the scale of the particle size of the foreign matter varies depending on the sensitivity of the photomultiplier 90. In this figure, L/
, L2. L, 3 is a threshold value of the level comparison circuit 102.

The level comparison circuit 102 compares the level of the detection signal with each threshold value, and outputs a binary code indicating the result of comparison with each threshold value. For example, if the detection signal level is the threshold Lll horizontal groove, (
000)2 is output, if the detection signal level is the threshold value 2 or more and the threshold value is less than 3, it outputs (011)2, and if the detection signal level is less than or equal to the threshold value L3, it outputs (111)2.

The output code of level comparison circuit 102 is input to an interface circuit tos that interfaces with data processing system 130.

The interface circuit 108 also receives information from the rotary encoder and the linear encoder to determine the rotation angle position O and the X direction ("I") at each time point.

A signal (binary code) indicating information on position X (radial direction) is inputted via buffer circuits 110 and 112.

Each input code to the interface circuit 108 is
- = taken into a certain register inside the interface circuit 108 at a constant cycle and temporarily held there.

Further, within the interface circuit 108, a stepping motor 14.2 is connected to the data processing system 130.
There is also a register in which control information for solenoid 87 and solenoid 87 is set. According to the control information set in this register, the motor controller 116 controls the stepping motor 14, 24, and the solenoid driver l17 controls the solenoid 87.

Further, a launch circuit 120 and a variable voltage dividing circuit 122 are provided to set the sensitivity of the photomultiplier 90. The variable voltage dividing circuit 122 divides a constant electric power, (2) supplied from the outside, at a dividing ratio according to the information held in the latch circuit 120, and applies the divided voltage to the photomultiplier 90. The partial pressure ratio can be switched to three levels: low sensitivity, medium sensitivity, and high sensitivity. The latch circuit 120 includes
Sensitivity designation information is set by data processing system 130 via interface circuit 108 .

Data processing system 130 includes microprocessor 13
1. Memory 1 for storing programs, data, etc.
32, a bus 133, a floppy disk device 134 for storing test result data, etc., its controller 136, a keyboard and a CRT display device for interacting with the operator, and a wafer foreign object map (not shown). X-Y for printing etc.
It consists of a plotter, etc.

This foreign matter inspection device has two operating modes: a normal mode in which each wafer is inspected once under set conditions, and a printout in the form of a foreign matter map on an X-Y plotter or display on a CRT display device. In addition to the automatic condition change inspection mode, in which each wafer is inspected for foreign matter multiple times while changing the inspection conditions (in this example, the sensitivity of the photomultiplier 90), and each inspection result is memorized and saved. Both operating modes can be specified from the keyboard. Since this automatic condition change inspection mode is directly related to the present invention, the operation in this mode will be explained below.

The wafer 30 is set at a predetermined position on the rotation stage 22, and when a set completion interrupt signal from the wafer automatic setting mechanism is given to the microprocessor 131 via the interface circuit 108, although the details are omitted, the microprocessor 131 loads the memory 132. According to the inspection processing program 132A, execution of the automatic condition change inspection mode process is started. The flow of the process will be explained along the flowchart of FIG.

First, the microprocessor 131
Motor control information for positioning the second stage 20 and the rotation stage 22 at predetermined positions, and the wafer 3
If the wafer 30 is a patterned wafer, move the S polarization cut filter 86 to the position 86'', and if the wafer 30 is a blank film wafer (or mirror wafer), move the S polarization cut filter 86 to the position 86''.
Solenoid control information for moving the polarization cut filter 86 to the solid line position is set in the internal register of the interface circuit 108 (step 200). In addition,
Whether the wafer has a pattern, a blank film, or a mirror surface is specified using the keyboard prior to inspection.

According to this motor control information, the motor controller 116
controls the stepping motors 14.24 to move each stage to a predetermined position. Similarly, the solenoid driver 117 controls the solenoid 87 according to the solenoid control information.
energize or deenergize.

Next, the microprocessor 131 writes 3 to 8 into the P counter 132C of the RAM 1321 (step 205).
, sets the value of the P counter 132C in the latch circuit 120 (step 210).

Since the information held by the latch circuit 120 is 3, ii) the voltage division ratio of the variable voltage divider circuit 122 becomes the highest, a voltage corresponding to low sensitivity is applied to the photomultiplier 90, and the sensitivity of the photomultiplier 90 becomes low sensitivity. Become.

Here, the value of the P counter 132C, that is, the sensitivity setting information, corresponds to the setting sensitivity of the photomultiplier 90. The memory 132 stores in advance conversion tables 1320°E and F between detection signal levels and foreign particle diameters corresponding to sensitivity curve data at low, medium, and high sensitivities.

Now, after completing the preparation process below, the actual inspection process begins.

First, the microprocessor 131 instructs the motor controller 116 to start scanning via the interface circuit 108 (step 215). Upon receiving this instruction, the motor controller 116 starts driving the motor 14.24 for the above-mentioned helical scan.

Next, the microprocessor 131 sequentially takes in the contents of a specific internal register of the interface circuit 108, that is, the code of the level comparison result of the detection signal (L code) and the code of the scanning position
2 specific area (step 220). Then, a zero test is performed for the L code (step 2
30).

If the L code is zero, it is determined that there is no foreign object at the current scanning position, and the process returns to step 220.

If the L code is not zero, the scanning position at that time is compared with the positions of other foreign objects that have already been detected and stored in the foreign object table 132G of the memory 132-H (step 235). If this comparison does not match, it is determined that a new foreign object has been detected, and the foreign object code is sent to P counter 1.
Convert according to the sensitivity using one conversion table corresponding to the value of 32C (setting sensitivity) (step 240), the code after the conversion, the information on the position of the foreign object, and the level comparison result code (information on the particle size of the foreign object) and the foreign matter table 132
G (step 245).

If the comparison in step 235 results in a match, it is determined that some of the foreign objects that have already been detected have been detected again, and information on the currently detected foreign object is not stored in the foreign object table 132G.

In parallel with this, the microprocessor 131 checks whether the scanning has progressed to the scanning end position based on the scanning position information taken in from the interface circuit 108 (step 225). When determining that the scan path is r, the microprocessor 131 sends a scan stop instruction to the motor controller 116 via the interface circuit 108 (step 250). In response to this instruction, motor controller 116 stops driving stepper motor 14.24! Make it.

Next, the microprocessor 131 executes the foreign object table 132.
The foreign object information stored in G is set to the setting sensitivity information +v(P
counter value) and wafer identification information to the floppy disk controller 136 and stored in the floppy disk device 134 (step 255).

Next, the microprocessor 131 controls the P counter 132
The value of C is decremented by 1 (step 260), and it is determined whether the value is less than or equal to 0 (step 265).

If 1t is greater than 0, the microprocessor 131 provides motor control information for positioning the wafer to a predetermined position to the motor controller 116 (step 270).

When the positioning is completed, the microprocessor 131
P instructs the motor controller 116 to start scanning.
The counter value is set in the latch circuit 120 (step 275). Then, the processing from step 215 onwards is started.

In this way, foreign object inspection is performed three times for each wafer. In the second test, the value of the latch circuit 120 is 2, so a voltage corresponding to medium sensitivity is applied to the photomultiplier 90 by the variable voltage divider circuit 122, and the medium sensitivity is set. Conversion table 132E is used for L code conversion. In the third test, the value of the latch circuit 122 is 1, so the photomultiplier 9
0 is set to high sensitivity, and the conversion table 132 for high sensitivity
F is used for L code conversion. Then, the data of each test period is stored in the floppy disk device once [1].

When the three IN inspections are completed, the result of the determination in step 265 becomes No, and the inspection for one wafer is completed.

In this way, foreign matter inspection is performed on the same wafer three times in total while changing the sensitivity of the photomultiplier 90, which is one of the inspection conditions, from low to medium to high, and the foreign matter inspection result data is stored on a floppy disk. The information is stored in the device 134. Then, the result data of such inspection or a foreign matter map based on the data is outputted using, for example, an X-Y plotter or a CRT display device, the optimum sensitivity is easily determined based on the data, and the optimum sensitivity is quickly and easily determined based on the result of the determination. can be set. Furthermore, it is also possible to select test result data with optimal sensitivity from among the test result data.

Note that the other operation modes are not directly related to the gist of the present invention, and therefore their explanations will be omitted.

Here, the present invention is not limited to the above-mentioned embodiments, but can be implemented with appropriate modifications.

For example, in the above embodiment, only the sensitivity is changed as the inspection condition, but other conditions such as the threshold for comparing the level of the output signal of the photomultiplier and the irradiation angle of the polarized laser beam may also be changed.

In the automatic condition change inspection mode, the foreign object map may be displayed on a CRT display device or the like during the inspection.

Scanning for inspection is not limited to spiral scanning, but may also be linear scanning, for example. However, since linear scanning stops at the scanning edge, the scanning time tends to increase, and when scanning a circular surface such as a wafer, position control at the scanning edge tends to become complicated. . Therefore, for foreign object inspection, such as wafers, helical scanning is generally advantageous.

Further, the present invention is also applicable to similar wafer foreign matter inspection apparatuses that utilize light beams other than polarized laser light.

Furthermore, the present invention is generally applicable to apparatuses that inspect people on the surface of objects to be inspected other than wafers.

[Effects of the Invention - 1] As described in detail, according to the present invention, foreign matter inspection of the same object to be inspected is repeated multiple times under different conditions, and the result data of each foreign matter inspection is stored in the storage means. Since the foreign object inspection device is given an operation mode to memorize, it can automatically obtain foreign object inspection result data under various inspection conditions, easily determine the optimum conditions from the result data, and quickly and easily perform the optimum operation. In addition to being able to set inspection conditions, if the optimal conditions are unclear, it is possible to select the foreign body inspection result data under the optimal conditions from the foreign body inspection result data obtained under various conditions obtained in such operation mode. It is possible to achieve effects such as significantly reducing the time and labor required for testing through manual intervention, compared to resetting conditions and retesting.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the optical system etc. of the wafer foreign matter inspection device according to the present invention, FIG. 2 is a schematic block diagram showing the signal processing and control system of the wafer foreign matter inspection device, and FIG. 3 is a schematic diagram of the wafer scanning system. The explanatory diagram, FIG. 4, is a graph showing the relationship between the particle size of foreign matter and the detection signal level, and FIG. 5 is a schematic flowchart of the automatic condition variation inspection mode. 10...X stage, 14.24...Stepping motor, 22...Rotation stage, 30...Wafer,
36.38...S polarized laser oscillator, 44.46...
・Cylindrical lens, 50...Detection system, 52...
・Microscope, 72...Slit, 86...S polarization cut filter, 90...Photomultiplier, 100・
...Amplifier, 102...Level comparison circuit, lO8...
- Interface circuit, 116... Motor controller, 120... Latch circuit, 121... Variable voltage divider circuit, 130... Data processing system, 131...
Microprocessor, 132...Memory, 134...
・Floppy disk device. Figure 3 Figure 4 Figure 11 Field a Mystery Figure 5 C=D ■

Claims (2)

[Claims] (1) A means for irradiating a light beam onto the surface of an object to be inspected, and a means for detecting a foreign substance on the surface of the object to be inspected based on reflected light from the surface of the object to be inspected; A foreign object inspection device that performs a foreign object inspection on the object to be inspected while scanning the surface, wherein the foreign object inspection on the same object to be inspected is repeated multiple times under different conditions, and the result data of each foreign object inspection is stored in a storage means. A foreign matter inspection device characterized by having a memorized operation mode. (2) The foreign matter inspection apparatus according to claim 1, wherein the object to be inspected is a wafer and the light beam is a polarized laser light beam.