JPS63122936A - System and apparatus for sampling detection signal of surface plate defect - Google Patents

Abstract

PURPOSE:To select and output a data of max. value in each cell by obtaining a defect detection signal of a face plate scanned by a scan line with circular arcs linked gradually at a fixed pitch. CONSTITUTION:A laser spot 1 herein used is oval with the long-axis radius sized DELTAr and a face plate 2 is divided into P areas of equal angle phicircumferentially and moves along the radius of the face plate 2 by one-Pth of DELTAr starting at the rotation center 0 of the face plate 2 each time it turns by an angle phi so that circular arcs are linked gradually at a pitch of DELTAr per turn. With this scanning, a measuring signal of an analog value continued as obtained by a defect detecting section is sampled by a sampling pulse (s). Then, each of the circular arcs by this scanning is divided by the length DELTAl, almost equal to the radius DELTAr of the spot 1 while being integer (n) times as much as a distance interval DELTAs of a pulse (s), to make cells. Max. value in the measurement data obtained by sampling for each cell is compared and selected to be outputted.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to a method and sampling device for sampling continuous measurement signals obtained by scanning the surface of a face plate such as a silicon wafer with a laser spot. .

[Prior Art] The conventional method for detecting defects on the surface of a face plate such as a silicon wafer is to irradiate a laser beam to form a spot on the surface and capture the scattered light caused by the defect using a light receiver. There is. In this case, there are two methods for scanning the laser spot: one is scanning in the X and Y axis directions, and the other is a rotation method in which the face plate is rotated to move the spot from the center or outer circumference in the radial direction. The rotary type has a simple optical system configuration and a simple scanning mechanism, and is advantageous when quickly inspecting a large face plate. In both formats, the defect data is displayed in numerical form as well as a map table 75 for determining the position of the defect.

Recently, semiconductor devices have become increasingly dense, and silicon wafer defect management has become more rigorous.In addition to improving defect detection capabilities, it is also required that numerical and map displays of data be highly accurate. has been done. In order to cope with these problems, it is necessary to perform effective scanning and sampling at a higher density than before, and to set the cell division described below more finely than before.

Now, in processing defect data, the surface of the face plate is divided into cells of appropriate microscopic area, and processing is performed based on this unit. For example, this cell unit is effectively used when one defect is sampled multiple times, when determining a single defect, or when determining whether a defect is isolated or continuous. . Note that when displaying the map, a plurality of cells are grouped together and a somewhat large range is displayed as a unit, taking into consideration the density of the display surface.

When dividing into cells like this, it is easy to use the X, Y scanning format to form cells of constant size. On the other hand, in the conventional method performed in a rotational manner, scanning is performed in a spiral manner outward from the center of rotation, and this scanning line is sampled at intervals of a constant rotation angle.

However, in this method, since the radius changes continuously as the face plate rotates, the angle θ and the radius r of the cell coordinates change simultaneously, making data processing complicated. In addition, sampling at a constant rotation angle requires a large distance interval between the outer peripheries of the face plate, so it requires some effort to configure cells of uniform size and high density. Furthermore, in a rotating type, if the rotational speed is constant, the scanning speed changes and becomes extremely high as it approaches the outer periphery, which is undesirable. Therefore, it is necessary to make the change in scanning speed as small as possible, that is, to gradually reduce the rotational speed toward the outer circumference.

In contrast to the conventional rotational scanning method described above, the radius of the scanning line is an arc that does not change within a certain angle Φ, and such arcs are connected in stages at each angle Φ. A scanning method in which the scanning line is spiral-shaped and the scanning speed is constant except near the center of rotation was filed at the same time by the same inventor as the present invention (patent application, White Plate Scanning Method for Laser Spots and White Plate Scanning Method). scanning control device). Therefore, there is a need for a method and apparatus that can set cells with as constant a size as possible and with a high density for such a hidden scanning line in which circular arcs are connected.

[Object of the Invention] The present invention solves the above-mentioned conventional difficulties in the rotation type, and uses a spiral scanning method in which circular arcs are connected in stages to set cells with a constant area. An object of the present invention is to provide a sampling method and a sampling device for a white board defect detection signal that selects and outputs data with the maximum value in a cell.

[Means for Solving the Problems] In the sampling method of the white board defect detection signal according to the present invention, an elliptical laser spot with a major axis radius of Δ is used as the scanning laser spot, and the white board is moved in the circumferential direction. niP
divided into areas of equal angle Φ, and each time the angle Φ is rotated,
This is a scanning method in which arcs are connected in stages at a pitch of Δ per revolution, starting from the rotation center of the white plate and moving in the radial direction of the face plate by 1 P of Δ.
A continuous analog measurement signal obtained by the defect detection section through the scanning is sampled by a sampling pulse S. The sampling pulse S is obtained by dividing the circumference of the face plate into equal angles ΔO by a large number N that is an integral multiple of the above P.

Next, each of the circular arcs resulting from the above scanning is approximately equal to the above ゛1'-diameter Δr of the laser spot, and an integer n (n is a variable) of the distance interval Δs of the sampling pulse S.
It is divided into cells having a double length Δl, and for each cell, data of the maximum value among the measurement data obtained by the above sampling is compared and selected and outputted.

Next, the sampling device according to the present invention realizes the above-mentioned sampling method, and a rotary encoder is directly connected to the spindle that rotates the white plate, and the rotary encoder outputs a zero signal indicating the reference point of the rotation angle according to the rotation. The ° pulse and the -1- sampling pulse S obtained by dividing the circumference of the white board into equal angles Δθ are output. These two pulses are input to a division signal generator, and a division signal B for dividing the face plate into the cells is output.

In the defect detection section, a continuous analog measurement signal is converted by scanning the laser spot, and in the sampling section, this signal is sampled by a sampling pulse S and converted into digital data to be used as measurement data. This measurement data is compared and selected in the comparator and latched in the data latch circuit, and the maximum value data of each cell is outputted by the classification signal B indicated by -1-.

The ``U'' classification signal generation section includes an n counter that counts 0@pulses and outputs a value for the radius of the scanning point, and a value for this radius that is input and calculates the length of the cell at the radius r. An nROM that outputs the number n of sampling pulses S included in Δl, sets this number n for each cell, counts the sampling pulses S, and outputs the above classification signal B when the counted number reaches n. n counter. In addition, the above comparison section sequentially inputs the measurement data from the above sampling, calculates the difference between the current measurement data (hereinafter referred to as this value) and the previous measurement data (hereinafter referred to as previous value), and the current value is the previous value. It consists of a subtracter that outputs a discrimination signal C when the value is larger than that, and a buffer A and a buffer B that temporarily store the current value and previous value, respectively.
Based on the above-mentioned discrimination signal C, the measurement data that is larger between the current value and the previous value is output. Next, the next measurement data is manually input to the buffer rA as the new current value, and -! The measurement data with a large value marked ``-'' is input to the subtracter and buffer B as a new previous value, and the same comparison as described ``2'' is repeated to compare and select the data with the largest value for each cell.

[Operation] In the sampling method according to the present invention described above, the face plate is divided into P pieces in the circumferential direction, and in each divided area, scanning lines forming concentric circular arcs are arranged at a pitch of Δ. ing. Each scan line is divided into cells of length Δr in the radial direction and Δl approximately equal to Δr in the circumferential direction. The shape of the cell is almost square, and by increasing the number N (by increasing the density of the sampling pulse S), it is possible to divide the entire face plate into cells with less variation in size. Furthermore, since each cell has the same radius value in one scanning arc, data processing based on cells can be performed efficiently.

Next, although the density of measurement data due to sampling gradually decreases from the center of rotation toward the outer periphery, the data with the maximum value is compared and outputted from the measurement data in the cells marked with "-". , a counting error in which one defect is sampled multiple times and is apparently output as a plurality of defects is eliminated by the high-density sampling pulse S. Further, since the size of each cell is substantially constant, defect data is output at a substantially uniform density for the entire face plate. This allows data processing, defect map display, distribution evaluation, etc. to be performed appropriately.

Next, in the sampling device according to the present invention, in order to realize the above sampling method, the number n of sampling pulses S included in the length Δl of each cell is counted at the radius r of the scanning position, A classification signal B is generated to classify the cells, and Δl is kept approximately constant. Note that the sampling pulse S is divided into P pulses by dividing the frequency of the sampling pulse S as an integer ratio convenient for frequency division between the above-mentioned division numbers P and N.

In the comparison section, the measured data that is manually generated at the sampling timing is compared with the current value and the previous value each time, the larger one is selected, and the maximum value data is changed for each cell. Thus, due to high-density sampling, a counting error in which one defect is sampled multiple times and is apparently output as multiple defects is avoided within the cell.
This is ineffective as a preprocessing process to obtain highly accurate defect data through advanced judgment in subsequent data processing.

[Example] Figures 1(a) and 1(b) show a laser spot scanning method according to the aforementioned patent application to which the sampling method and sampling device for the face plate defect detection signal according to the present invention are applied. A laser spot 1 with a radius Δ rotates in the direction of arrow A and moves by a distance δ=Δr/P in the radial direction of the face plate 2 for every angle Φ=2π/P. In the area of the angle Φ, the scanning lines 3 are concentric arcs with a pitch of Δ, which are connected in stages to form a spiral. Figure (b) shows the intensity distribution of laser spot 1. Due to the characteristics of the laser spot, %1''-diameter Δr is defined as a value of 1/e2 with respect to the central value of the intensity, and this is defined as Δr.
shall be. By scanning with a pitch of Δ, adjacent scanning lines 3
Laser spots 1 and 1' at positions 1 and 3' overlap as shown, and scanning with relatively small intensity changes is performed.

However, in this case, the same defect is detected twice by adjacent scanning lines 3 and 3', resulting in a detection error. Such double errors can be eliminated by separately processing data between cells.

FIG. 2 shows a sampling pulse S and a cell setting method for the sampling pulse S in an embodiment of the sampling method and sampling device for the face plate defect detection signal according to the present invention. A laser spot 1 scans along an arcuate scanning line 3, and the obtained defect detection signal is sampled by a sampling pulse S. Take the length Δl, and set the value of n so that the sampling pulse S/''Sn is included within Δl. Note that Δl is approximately equal to Δr. On the other hand, in the radial direction of {11}, the scanning line 3 is A patent characterized by a length Δr as the center and a range divided by these.If the angle of equal division in the circumferential direction of the face plate is Δθ, then Δs=rΔθ, and Δs changes in proportion to the radius r. Therefore, the ROM is used to store n for r in advance, and the cells 4 are classified.

FIG. 3 is a block diagram of a circuit configuration in an embodiment of the sampling method and sampling device for face plate defect detection signals according to the present invention. , a continuous measuring signal of an analog quantity is changed by scanning the laser spot. In the sampling section 7, the measurement signal is sampled by the above-mentioned sampling pulse S, converted into a digital quantity, and transferred to the comparison section 8 as measurement data. In the comparator 8, at the timing of the sampling pulse S, the sequentially inputted measurement data is compared and selected within the cell 4, and latched into the data latch circuit 9.

On the other hand, the rotary encoder 10 directly connected to the rotational movement mechanism 6 outputs a 0'' pulse indicating the reference point of the rotation angle and a sampling pulse S. These two pulses are input to the segmentation signal generator 11 and then A division signal B is generated, whereby the data latched in the data latch circuit 9 is outputted as the maximum value data of each cell.

FIG. 4 is a detailed block diagram of the comparator 8 in FIG. 1, and when the current value is larger than the previous value, a discrimination signal C is output from the terminal 8-2. On the other hand, the current value is input to the subtracter 8-1 and the buffer yA8-3, and at the same time, the data already stored in the buffer A is transferred to the buffer B8-4 as the previous value, but the discrimination signal C is generated. When this happens, the current value is large, so the discrimination signal C is applied to the buffer A as a strobe, and the current value is latched into the F latch circuit 8-5. This current value is transferred to the data latch circuit 9 at the next timing, and simultaneously input to the subtracter 8-1 and buffer B as the previous value. Conversely, when the previous value is larger than the current value, the discrimination signal C is not output, but the output level of the terminal 8-2 is inverted and applied to the buffer B as a strobe, and the previous value is sent to the F latch circuit 8-5. be transferred.

At the next timing, this previous value is transferred to the data latch circuit 9, and is also transferred to the subtracter 8-1 and buffer B again to become the previous value for the next comparison. In this way, the data latch circuit 9 is updated by inputting large data selected by successive approximation, and the maximum value data in the cell is outputted by the division signal B.

FIG. 5 is a detailed block diagram of the division signal generating section 11 in FIG.
The @ signal is counted by the n counter 11-1 and outputs the value of the radius of the scanning point. The value of n corresponding to r is set in the nROM 11-2 in advance, and the value of 11 is outputted according to the value of 2 manually set, and the value of n is outputted to the n counter 11-2.
Set to 3. The sampling pulse S is manually counted by the n counter, and when the count reaches H, the division signal B is output and applied to the data latch circuit 9 as described above. Note that at the time of starting the rotation, the rotation mechanism 6 starts rotating from an arbitrary angle, and the n counter 11-1 shows 0.
``Since the pulse is not manually generated, the value of n is not set in the n counter from the nROM.Therefore, the initial value of n is preset before starting.

In addition, in order to accurately classify the cells, the 0° pulse is
It is necessary to synchronize with any one of the sampling pulses S, and it is easy to add such a synchronization circuit if necessary.

Referring again to FIG. 3, the data of the maximum value described above is temporarily stored in the data buffer 12, and is then transferred to the data processing device 17.
However, in order to determine the defect mentioned earlier or to display a map, it is necessary to add its position coordinates to the defect representative data.

In FIG. 3, the n counter 1 in the division signal generator 11
The value of the radius obtained by 1-1 is temporarily stored in the R buffer 14, and the sampling pulse S is counted by the θ counter 16, and the obtained value of θ is stored in the θ buffer 1.
5 is temporarily stored.

The classification signal B is input to the entry timing circuit 13 to output a strobe signal to be applied to the data buffer 12, R buffer 14 and 0 buffer 15, and each data is transferred to the data processing device 17.

FIG. 6 is a schematic flowchart showing the operating procedure of each part in FIG. 3. When the inspection for face plate defects is started at step (2), the laser spot moves to the center position (2) and the face plate rotates (2). A 0° pulse is output from the rotary encoder (2), which is input to the R counter and counted, and the value of the radius is output (2) and transferred to the n ROM. nRO
The value of [l corresponding to r from M is read out and set in the n counter, but the input sampling pulse S
When reaches n, division signal B is output.

On the other hand, the measurement signal output [phase] obtained by the defect detection scan ■ is the sampling pulse S from the rotary encoder.
It is sampled and A/D converted by ■
Then, the data of the maximum value resulting from the comparison and selection is outputted by the classification signal B [phase], processed in the data processing device, and displayed on a map (2). Note that the sampling pulse S is 0
The counter counts and outputs 0 data [phase], which is added to the maximum value data (h) and used for data processing, along with the value 2 output by the R counter.

[Effects of the Invention] As is clear from the above description, according to the sampling method and sampling device for the face plate defect detection signal according to the present invention, the face plate defect detection signal can be scanned by a scanning line in which arcs with a constant pitch are connected in stages. By applying this method to the defect detection signal of the face plate, it is possible to form cells that are subdivided into two parts with a substantially constant shape and area. Since the defect data is the maximum value in the cell, counting errors are eliminated for a single defect in the cell.Also, since the area of each cell is almost constant, for the entire area of the face plate, It is possible to display a map of the distribution of defects with more precision and uniform density than ever before. Furthermore, since the coordinate r of each cell is constant for each circular arc, software programming is simple in advanced data processing performed between each cell, which is useful for constructing a highly accurate face plate defect detection device. It has a remarkable effect on

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are explanatory diagrams showing the scanning line by the laser spot and the intensity distribution of the laser spot to which the sampling method and sampling device of the face plate defect detection signal according to the present invention are respectively applied, and FIG. , an explanatory diagram of a method for configuring cells from sampling pulses in the sampling method and sampling device for the face plate defect detection signal according to the present invention; FIG. A block diagram of an embodiment of
4 is a partial block diagram of FIG. 3, FIG. 5 is a partial block diagram of FIG. 3, and FIG. 6 is a flowchart showing the operation procedure of each part with respect to FIG. 1... Laser spot, 2... Face plate, 3...
- Scanning line, 4... Cell, 5... Face plate defect detection section, 6... Rotation movement mechanism, 7... Sampling section, 8... Comparison section, 8-1... Subtractor, 8-2...Terminal, 8-3...Buffer A
1 8-4...Buffer B. 8-5...F latch circuit, 9...Data latch circuit, 10...Rotary encoder, 11-...Division signal generator, 11-1...R counter, 11-2...nROM , 11-3...n counter, 12...data buffer, 13...entry timing circuit, 14-...R buffer, 15...0 buffer, 16...θ counter, 17... Data processing equipment.

Claims (4)

[Claims] (1) A laser spot with a radius of Δr in the major axis direction and an elliptical cross section is divided into P areas of equal angle Φ in the circumferential direction of the surface of the face plate, with the rotation center of the face plate as the starting point. Angle Φ
Each time it rotates, it moves step by step in the radial direction of the face plate and in the long axis direction by one P/P of the radius Δr to scan the surface of the face plate in a spiral shape in which circular arcs are connected in stages. In the faceplate scanning method, continuous analog measurement signals obtained in the defect detection section by the scanning are measured by dividing the circumference of the faceplate by an equal angle Δ by a large number N that is an integer multiple of the above P.
Sampling is performed with a sampling pulse S divided into θ,
Each of the scanning lines forming the above-mentioned circular arc is divided into cells with a length Δl that is approximately equal to the above-mentioned radius Δr of the laser spot and an integral number n times the distance interval Δs of the sampling pulse S, and the above-mentioned sampling A sampling method for a face plate defect detection signal, which is characterized by outputting the maximum defect data for each cell from among the obtained measurement data. (2) A 0° pulse that is directly connected to the spindle that rotates the face plate and indicates the angle reference point, and a 0° pulse that indicates the angle reference point and the circumference of the face plate as the number N
a rotary encoder that outputs the sampling pulse S for every angle Δθ equally divided by , and a division signal generator that receives the 0° pulse and the sampling pulse S and outputs a division signal B that divides the face plate into cells. a sampling section that samples the analog measurement signal output from the defect detection section using the sampling pulse S and converts it into digital measurement data; and a comparison section that compares and selects the sampled measurement data for each cell. and,
A sampling device for a face plate defect detection signal, comprising a data latch circuit that latches the comparatively selected data and outputs the maximum value data of each cell based on the classification signal B. (3) An R counter that counts the 0° pulses and outputs the value of the radius of the face plate at the scanning point, and an R counter that inputs the value of the radius r and calculates the value of each cell corresponding to the value of the radius r. an nROM that outputs the number n of each of the sampling pulses S included in the length Δl, sets the value of the number n, counts the sampling pulses S, and outputs the classification signal B when it reaches n; 3. The face plate detection signal sampling device according to claim 2, further comprising the division signal generating section, which comprises an n counter. (4) Sequentially input at the sampling timing of the above measurement data, calculate the difference value between the current measurement data and the previous measurement data, and when the value of the current measurement data is larger than the value of the previous measurement data, the discrimination signal C A subtracter that outputs the data, and a buffer A that inputs and temporarily stores the current measurement data.
and a buffer B that temporarily stores the previous measurement data, and outputs the measurement data of the larger value between the current measurement data and the previous measurement data according to the above-mentioned discrimination signal C,
The present invention has the above-mentioned comparing section, which inputs the next measurement data as new current measurement data into buffer A, and inputs the above-mentioned large measurement data into the subtractor and buffer B as new previous measurement data. Range 2nd
A sampling device for a face plate defect detection signal as described in 2.