JPH0754819B2 - Foreign matter inspection device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign matter inspection apparatus for inspecting foreign matter on the surface of a wafer of an integrated circuit.

[Prior Art] In a conventional foreign matter inspection apparatus, as a management information of foreign matter inspection data of individual wafers, a wafer identification information unique to each wafer is input by an operator through an input means such as a keyboard. .

[Problems to be Solved] However, there is a problem that the operation of inputting the wafer identification information is troublesome and an error is likely to occur due to an incorrect input of the wafer identification information.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a foreign matter inspection apparatus that does not require manual input of wafer identification information and prevents an error due to an error in the wafer identification information. .

[Means for Solving Problems] On a wafer of an integrated circuit, wafer identification information (numerals, letters, and other symbols) is imprinted on the orientation flat (abbreviated as orientation flat in this specification) portion. It is recorded by the method such as.

In view of this point, the present invention relates to a foreign matter inspection apparatus for inspecting a foreign matter on the surface of a wafer, an image sensor for picking up an image of the wafer, a means for detecting an angle of an orientation flat of the wafer,
A means for cutting out a character image of the wafer identification information recorded on the wafer from the image information of the wafer obtained by the image sensor with reference to the angle of the orientation flat detected by this means, and a character image cut out by this means. And a means for recognizing characters.

[Operation] According to the present invention, since the wafer identification information recorded on the wafer is read by the above-described configuration, it is not necessary to manually input the wafer identification information, and an error due to an error in the wafer identification information can be eliminated. It can be prevented.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view of an embodiment of the foreign matter inspection apparatus according to the present invention, and shows only a portion directly related to the gist of the present invention.

In this figure, 10 is a wafer and 10a is its orientation flat. Reference numeral 10b denotes a wafer identification information recording unit in which wafer identification information is recorded as a combination of characters, numbers, symbols, etc. by stamping or the like. This wafer identification information recording section 10
The relative position between the character etc. recorded in b and the orientation flat 10a is predetermined.

Reference numeral 12 is a rotary chuck that rotates the wafer 10 by fixing it by negative pressure suction. In this embodiment, this rotary chuck
Although not shown in the figure, 12 is provided in the pre-alignment stage, and there is a mechanism in the vicinity thereof for gripping the semiconductor wafer 10 and carrying it to the inspection stage. The rotary chuck 12 may be a rotary chuck of an inspection stage.

14 is a motor for driving the rotary chuck 12, 16
Is a motor drive circuit for driving it. Reference numeral 18 denotes a rotary encoder that detects the rotation angle of the rotary chuck 12. In this embodiment, the rotary encoder 18 is an absolute type encoder and outputs the detected rotation angle as digital data.

20 is a one-dimensional CCD for imaging the outer peripheral portion of the wafer 10.
It is an image sensor, and is arranged so that the outer peripheral portion of the wafer 10 is within the visual field. Wafer identification information recording unit 10
b also comes into this view. The CCD image sensor 20 has a field of view whose longitudinal direction coincides with the radial direction of the rotary chuck 12 and crosses the outer peripheral edge portion of the wafer 10 at a substantially right angle.

Although there are means for illuminating the surface of the wafer 10 and an objective lens for focusing the reflected light from the surface of the wafer 10 on the CCD image sensor 20, they are omitted in the figure.

An image sensor drive circuit 22 drives the CCD image sensor 20, and generates drive pulses (start pulse, shift clock pulse) for the CCD image sensor 20. The CCD image sensor 20 is scanned in the direction of arrow X, which coincides with the radial direction of the rotary chuck 12.

A binarization circuit 24 binarizes the output image signal (image information) of the CCD image sensor 20 at a predetermined threshold level THa.
This threshold level is lower than the image signal level corresponding to the wafer surface and higher than the image signal level corresponding to the character line portion such as numbers, letters and other symbols recorded in the wafer identification information recording section 10b. Is set.

A serial / parallel conversion circuit 26 converts a bit pattern (binary image information of the wafer) serially output from the binarization circuit 24 into a parallel bit pattern.

28 is a CPU, 30 is its bus, and 32 is a memory for storing programs and data. Reference numeral 34 is an input / output interface circuit. Through this input / output interface circuit 34, the CPU 28 can access the image sensor drive circuit 22, the register 26 and the motor drive circuit 16.

FIG. 2 is a schematic flowchart of the wafer identification information reading operation in this embodiment. The operation will be described below with reference to this flowchart.

When the wafer 10 is fixed to the rotary chuck 12 by negative pressure suction, the CPU 28 activates the motor drive circuit 16 to drive the motor 1
4 is driven at a constant speed, and the rotary chuck 12 starts rotating at a constant speed.

Thereafter, the CPU 28 executes the wafer identification information reading operation program shown in FIG.

First, in step 1, the CPU 28 activates the image sensor drive circuit 22 at regular intervals, the CCD image sensor 20 is scanned, and the image signal (wafer image information)
Is output serially. This image signal is binarized by the binarization circuit 24 and converted into a parallel bit pattern by the serial / parallel conversion circuit 26.

In this bit pattern, the bit corresponding to the position outside the outer peripheral edge of the wafer 12 and the bit corresponding to the character line part of the recorded character of the wafer identification information part 10 are "0", and the other bits are "1". .

Now, the CPU 28 reads the bit pattern output from the serial / parallel converter 26 and the output data θ of the encoder 18 after the scan of the CCD image sensor 22 is completed, and pairs them into the input table 36 on the memory 32. Store sequentially.

By repeating the same operation, various rotation angles θ and bit patterns (binary image information) of image signal data at the angles are collected in the input table 36. When the data for one rotation or more of the rotary chuck 10 is collected, this step is ended and the process proceeds to the next step 2 and subsequent steps.

Steps 2 to 6 are processing steps for detecting the angle of the orientation flat 10a of the wafer 10 based on the data collected in the input table 36.

First, in step 2, each bit pattern stored in the input table 36 is referred to, and "1" on the most upper side (the side which is output earlier from the CCD image sensor 20) is referred to.
Is detected as the outer peripheral edge position x of the wafer (position in the radial direction of the rotary chuck), and the numerical data indicating the outer peripheral edge position is paired with the data of the corresponding rotation angle θ to form an edge table on the memory 32. Store in 38.

When the edge table 38 is created in this way, the process proceeds to step 3. Here, description will be given with reference to FIG.

When the rotation angle θ of the rotary chuck 12 is plotted on the horizontal axis and the outer peripheral edge position x recorded in the edge table 38 is plotted, for example, a curve L ₁ in FIG. 2 is obtained. The mountain portion of the curve L _{1 at} the outer peripheral edge position corresponds to the orientation flat portion of the wafer.

By the way, since the wafer can be regarded as a perfect circle except for the orientation flat portion, the outer peripheral edge position x should be constant in the portion other than the orientation flat portion of the wafer unless there is eccentricity between the wafer and the rotary chuck. The plot of is like the curve L ₂ . However, in actuality, as shown in the curve L ₁ , the outer peripheral edge position x fluctuates even outside the orientation flat portion. This fluctuation is due to the eccentricity of the wafer and the rotary chuck, and the overlapping of the fluctuation due to the eccentricity causes the peak of the curve L ₁ corresponding to the orientation flat portion to deviate from its original position. Therefore, if the angle of the orientation flat is detected from the curve L ₁ without removing the variation due to eccentricity, the detection error will be large.

The fluctuation component due to the eccentricity appears as a sine wave as shown by the curve L ₃ in FIG.

Therefore, in this embodiment, a process of extracting the fluctuation component of the outer peripheral edge position due to the influence of such eccentricity and excluding the fluctuation component from the data of the outer peripheral edge position is performed. Then, the orientation flat angle is detected based on the processed outer edge position data (corresponding to the curve L ₂ ).

Now, in step 3, the Fourier analysis processing of the data stored in the edge table 38 is performed, and the sinusoidal variation component (the component corresponding to the curve L ₃ ) due to the influence of the eccentricity as described above is extracted.

In the next step 4, the processing for removing the eccentric component extracted in step 3 is performed on the data of the outer peripheral edge position stored in the edge table 38. As a result, the outer edge position data corresponding to the curve L ₂ with the influence of eccentricity removed is obtained in the edge table 38.

In the next step 5, referring to the data of the edge table 38, the angle θa at which the plot curve L ₂ of the outer peripheral edge position excluding the influence of eccentricity intersects with the specific threshold level THb,
A process of detecting θb is performed.

In the next step 6, an intermediate angle θc between the angles θa and θb is calculated as an orientation flat angle.

As described above, according to the present embodiment, the orientation flat angle detection is performed based on the stored data in the edge table after the processing for eliminating the fluctuation of the outer peripheral edge position due to the influence of the eccentricity between the wafer and the rotary chuck. Even if the eccentric amount between the wafer and the rotary chuck is large, the orientation flat angle can be detected with high accuracy.

It should be noted that such orientation flat angle detection is performed not only for extracting characters from wafer identification information, which will be described later, but also for rotating chucks.
This is also for aligning the angle of the wafer 10 by controlling the stop angle of 12. According to this embodiment,
Even if the eccentricity between the wafer and the rotary chuck is large, the orientation flat angle can be detected with higher accuracy than before, so that the accuracy of the wafer angle alignment is improved.

Now, when the orientation flat angle is detected, the process proceeds to the character reading process from step 7.

In step 7, the image information of the characters (numbers, letters, and symbols) of the wafer identification information is cut out one by one from the set of bit patterns (image information of the outer peripheral portion of the wafer) in the input table 36, and the characters in the memory 2 are extracted. Store in buffer 40. Since the relative position between each character of the wafer identification information and the orientation flat 10a is predetermined, the position of the cutout area of each character is calculated with the orientation flat angle θc as the position reference.

When one character image information is cut out, the process proceeds to step 9. In this step, the character feature is extracted from the character image information in the character buffer 40, and this feature and the dictionary 42 are extracted.
Characters are recognized by collating with the characteristics of various characters registered in the memory 32 (this is preloaded in the memory 32 from a floppy disk device (not shown) or the like). The character recognition result is stored in a specific area of the memory 32.

Since such character recognition processing is known in the field of optical character recognition devices and the like, further description will be omitted.

When the recognition of the cut out characters is completed, it is determined whether there are any remaining characters (step 9). Although not shown in the flow chart of FIG. 2, the termination is determined by counting the number of cut characters and comparing with the number of characters (predetermined) in the wafer identification information. If there are remaining characters, the process returns to step 7 to cut out the next character image information and perform character recognition. The operation ends when the last character is recognized.

FIG. 4 is a schematic diagram of another embodiment of the present invention. In this figure, the same parts as those in FIG. 1 are designated by the same reference numerals.

The difference in the configuration from the above embodiment is that the output image signal (image information) of the CCD image sensor 20 outputs an edge detection signal when it exceeds a specific threshold level THc, and an edge detection circuit 44,
When this edge detection signal is generated, a register 46 for latching the output data (scan address) of the scan address counter 22a in the image sensor drive circuit 22 is added, and the data held by this register 46 (scan address) is the outer peripheral edge position. This is a point input to the CPU 28 as x data.

The threshold level THc is set to be higher than the image signal level corresponding to the outside of the wafer and lower than the image signal level corresponding to the inside of the wafer. Therefore, the register
The scan address latched by 46 corresponds to the outer peripheral edge position x of the wafer.

FIG. 5 is a schematic flowchart of the wafer identification information reading operation in this embodiment.

Step 11 is a processing step similar to step 1 in the above embodiment. However, serial / parallel converter
Not only the output bit pattern of 46 and the data of the angle θ are written in the input table 36, but also the held data (scan address) of the register 46 and the data of the angle θ are written in the edge table 38. Therefore, in this embodiment, step 2 of the edge table creating process in the above embodiment is not necessary.

The following steps 12 to 18 are the same processing steps as steps 3 to 9 in the above embodiment.

Although the two embodiments have been described above, the present invention is not limited thereto.

For example, the functions performed by the program processing may be realized by hardware or firmware.

Also, the output image signal of the image sensor is stored in the memory as multi-gradation image information through an analog / digital converter,
From this image information, the same processing as in each of the above-described embodiments can be performed.

The method of extracting the fluctuation component of the outer peripheral edge position due to the influence of eccentricity may be appropriately changed. Further, when the amount of eccentricity is sufficiently small, extraction of the fluctuation component and correction of the edge data can be omitted.

The method of detecting the orientation flat angle can be changed. For example, the angle of two points at which the detection signal of the capacitance displacement meter facing the outer peripheral portion of the wafer crosses a predetermined threshold level is detected.
The angle between the points may be detected as the orientation flat angle.

Further, although the one-dimensional CCD image sensor is used in the above-described embodiment, another one-dimensional image sensor or two-dimensional image sensor can be used.

Besides, the present invention can be appropriately modified and carried out within the scope not departing from the gist thereof.

[Effects of the Invention] As is apparent from the description related to the above embodiments, since the present invention is configured to automatically read the wafer identification information recorded on the wafer, it is necessary to manually input the wafer identification information. Is unnecessary, the operability of the foreign substance inspection apparatus is improved, there is no concern about erroneous input of wafer identification information, and there is an effect that a foreign substance inspection data management error due to an error in wafer identification information can be prevented. is there.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, FIG. 2 is a schematic flowchart of a wafer identification information reading operation, and FIG. 3 is an outer peripheral edge position, a variation component due to eccentricity, and an outer periphery edge position excluding the variation component. FIG. 4 is a schematic diagram of another embodiment of the present invention, FIG.
The figure is a schematic flow chart of the wafer identification information reading operation in the other embodiment. 10 ... Wafer, 10a ... Orientation flat, 10b ... Wafer identification information recording unit, 12 ... Rotary chuck, 18 ... Rotary encoder, 20 ... One-dimensional CCD image sensor, 22 ... Image sensor drive circuit, 22a ... ... Scan address counter, 24 ... Binarization circuit, 26 ... Serial / parallel conversion circuit, 28 ... CPU, 32 ... Memory, 44 ... Edge detection circuit, 46 ... Register.

Claims (1)

[Claims] 1. A foreign matter inspecting apparatus for inspecting foreign matter on a surface of a wafer, comprising: an image sensor for picking up an image of a wafer; a means for detecting an angle of an orientation flat of the wafer; and an angle of the orientation flat detected by this means as a reference. A unit for cutting out a character image of the wafer identification information recorded on the wafer from the image information of the wafer obtained by the image sensor, and a unit for recognizing the character image cut out by this unit. Foreign matter inspection device.