JP3575574B2 - Foreign object inspection system for patterned wafers - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a foreign matter inspection apparatus for a patterned wafer, and more particularly, to a foreign matter inspection apparatus capable of detecting foreign matter with higher accuracy in a foreign matter inspection apparatus for a patterned wafer using an XY scanning method.
[0002]
[Prior art]
In the IC manufacturing process, if foreign matter adheres to the surface of the wafer or various patterns forming the semiconductor region, insulating region, electrodes, wiring, etc., the performance of the IC deteriorates. The apparatus inspects foreign matter on the wafer.
The wafer foreign matter inspection apparatus includes an XY scanning method in which the wafer surface is irradiated with a laser beam to scan the wafer in the X and Y directions, and a wafer is rotated by irradiating the laser beam to spirally or concentrically rotate the wafer. There is a rotation scanning method for scanning.
[0003]
FIG. 4A shows an example of the configuration of a rotary scanning type wafer foreign matter inspection apparatus. In the drawing, reference numeral 1 denotes a patterned wafer having IC chips 11 on which a large number of patterns are formed. The wafer 1 is attracted and fixed to the rotation stage 21 of the rotation mechanism 2. The laser beam L from the two laser light sources 31A and 31B of the light projecting unit 3 is applied to the surface of the wafer 1. _T Are irradiated at a low angle in the X direction. The irradiated laser beam is spotted by the focusing lenses 32A and 32B. _P To form a foreign matter detection area on the wafer 1. The wafer 1 is rotated in the θ direction by the motor (M) 22 controlled by the control circuit 25. Further, the XY moving mechanism 23 continuously moves in the Y direction or feeds the image in steps. As a result, the surface of the wafer 1 _P Is scanned spirally or concentrically.
This spot S _P , The foreign matter adhering to the surface of the wafer 1 and the pattern are both scattered light L _R Are collected by the condenser lens 41 of the light receiving unit 4. For example, the light is received by a light receiving unit 42 including a CCD image sensor and an amplifier. The light receiving section 42 is provided with the scattered light L _R Is output as a detection signal.
[0004]
On the other hand, the rotary encoder 24 and the control circuit 25 directly connected to the motor 22 of the rotation mechanism 2 have moved in the Y direction and the angle signal θ indicating the rotation angle of the wafer 1 as shown in FIG. Spot S _P And a position signal R indicating the scanning position is output, and the respective outputs are input to the foreign matter detector 5 together with the luminance signal i.
At this time, the foreign matter detection unit 5 has received an appropriate threshold value V from the microprocessor (MPU) 63 of the data processing unit 6 in advance. Therefore, the luminance signal i input to the foreign substance detection unit 5 is compared with the threshold value V, and thereby the foreign substance is detected. The foreign matter detection signal (data) is further added to the data of the rotation angle θ of the wafer 1 and the data of the scanning position R to form foreign matter data, and is once transferred to the buffer memory 61 of the data processing unit 6 and stored.
When the detection of foreign substances on the entire surface of the wafer 1 is completed, the stored foreign substance data is converted from Rθ coordinates to XY coordinates by the coordinate conversion section 62 and displayed on the output section 7 composed of a CRT display or the like on a map.
[0005]
As shown in FIG. 4C, the relationship between the wiring pattern and the like formed on the IC chip 11 and the irradiation light is such that the pattern PT is parallel or perpendicular to the orientation flat (OF) of the wafer 1. It is formed in the direction. On the other hand, the foreign matter Q is randomly scattered in the pattern PT and other plain portions. Scattered light L of both _R Has a characteristic, and the foreign matter Q generates omnidirectional scattered light corresponding to its size. On the other hand, the scattered light of the pattern PT is stronger at the edge E than at its surface, and has directivity depending on the direction of the pattern PT. It is shown in FIG. In the figure, θp is about 22.5 ° from the X axis and the Y axis. Angle. This angle The scattered light of the pattern PT concentrates on a portion indicated by a mesh line as a specific range as a center.
FIG. 6 shows an example of the waveform of the luminance signal i at this time. One method of detecting the foreign matter Q will be described with reference to FIG. The luminance signal i input to the foreign substance detection unit 5 is sampled at an appropriate angle δθ. In the specific range centered at about 22.5 ° as described above, the waveform of the luminance signal due to the scattered light of the pattern PT has a considerably large amplitude. ₂ Are superimposed. On the other hand, there is a noise N in a solid portion other than the pattern PT, ₁ The pulse is riding.
[0006]
For convenience of explanation, FIG. 6 shows the waveforms of the high-level luminance signal and the luminance signal of the plain portion in the pattern in the specific range, respectively. Of course, there is a waveform having a level of.
Therefore, the data control unit 6 sets a fixed threshold V slightly larger than the noise N for the luminance signal i. ₁ Is set in the foreign matter inspection unit 5, the foreign matter Q ₁ Is naturally detected. However, foreign matter Q ₂ And the pattern PT are both detected, so that the portion of the pattern PT is detected as a foreign substance. That is a false alarm in foreign object detection. Therefore, the data control unit 6 sets the threshold V ₁ Instead of the fixed threshold V slightly larger than the pattern PT ₂ Set. In this case, foreign matter Q ₁ Is not detected, resulting in a detection error. In any case, the fixed threshold V ₁ , V ₂ Is not appropriate.
As a solution to such a problem, it is conceivable to perform a foreign substance inspection by dynamically changing a threshold value according to the level of the luminance signal i. In this regard, Japanese Patent Application Laid-Open No. Hei 7-243977, entitled "Method of Calculating Floating Threshold for Foreign Object Detection," and Japanese Patent Application Laid-Open No. Hei 7-243977, "Apparatus for inspecting foreign matter on patterned wafer," have already been filed by the applicant of the present application.
[0007]
Next, the configuration of the XY scanning type foreign matter inspection apparatus will be described with reference to FIG. In the XY scanning method, the motor 22 which is a rotation mechanism of the wafer 1 in FIG. 4 is used simply for performing alignment so that the orientation flat is parallel to the X axis or the Y axis. The XY scanning is performed by the XY moving mechanism 23. In addition, the light projecting unit 3 is usually provided with one of the laser beams L of the laser light sources 31A and 31B. _T Is used. Further, in the XY scanning method, instead of the angle signal θ and the position signal R, the X and Y coordinates are sent from the control circuit 25 or the MPU 63 to the foreign matter detection unit 5. Then, the coordinate conversion unit 62 is deleted.
In the XY scanning type foreign matter inspection apparatus, the control circuit 25 drives the motor 22 to position the orientation flat of the wafer 1, and when this is completed, the control circuit 25 drives the XY moving mechanism 23 to perform XY scanning. Do. Then, foreign matter detection is performed at each scanning point.
[0008]
[Problems to be solved by the invention]
Now, in any of the scanning methods, and even if the threshold value is dynamically changed as in the above-mentioned application, the light receiving condition of the light receiving element fluctuates, or the optical detection condition fluctuates or differs. Then, it was found that the pattern was erroneously detected as a foreign substance.
In addition, since the dynamic threshold setting in the above-mentioned application is obtained by using a sample wafer of the same kind as the wafer to be inspected, a difference occurs in the inspection conditions and the light receiving level is shifted from the actual wafer to be inspected. Tends to occur. This also tends to cause erroneous detection of foreign matter.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a foreign matter inspection apparatus for a patterned wafer that can detect foreign matter with high accuracy.
[0009]
[Means for Solving the Problems]
The patterned wafer foreign matter inspection apparatus of the present invention that achieves the above object irradiates a patterned wafer having a pattern formed as an IC chip with a laser beam at a predetermined angle and receives the scattered light, In a foreign matter inspection device that obtains a detection signal corresponding to the level of the received light and detects foreign matter in accordance with the detection signal, a level that converts the level of the detection signal in a certain chip into one of a plurality of multi-level levels A conversion circuit, and a signal obtained by receiving the signal indicating the level converted by the level conversion circuit and converting the detection signal at a similar position of a chip adjacent to the certain chip by the level conversion circuit. A judgment circuit for judging the presence or absence of a foreign object by comparing with a signal indicating the level A predetermined range is set for a similar position of the adjacent chip, and a signal indicating the converted level in the adjacent chip is a maximum value selected from the predetermined range. Things.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
As described above, according to the present invention, the detection signal, that is, the detection signal (luminance signal) is converted into one of a plurality of multi-level levels including a plurality of predetermined steps, that is, so-called multi-level conversion is performed. The obtained level is compared with a converted level obtained by similarly multi-leveling a luminance signal (detection signal) at a similar position of an adjacent chip. In this way, the level of the comparison reference value can be obtained each time from the adjacent chip without being fixed. That is, according to the present invention, the foreign matter detection threshold can be obtained in a state where the foreign matter detection threshold dynamically changes according to a light receiving condition or an inspection condition according to a place to be inspected. In addition, since the conversion values are set in multiple stages, even if the conversion values fluctuate according to the light receiving conditions or inspection conditions, the luminance signals of the chip on the foreign matter detection side and the adjacent chip serving as a comparison reference for the chip are Since there is a similar variation, there is almost no relative variation in the converted value as a comparison condition.
It should be noted that even if the level conversion to the multi-valued level is performed on the analog detection signal itself (to be described below as a luminance signal), the luminance signal is A / D converted and once digitized to a converted digital value. You may go to. The embodiment described below is the latter case.
[0011]
By the way, when the inspection target is a pattern, large scattered light is generated, and the level of the luminance signal is increased. According to the present invention, since the target for obtaining the comparison reference value is the adjacent chip, the place where the luminance signal is obtained is different. Therefore, there may be a case where only a low comparison reference value is obtained. In such a case, when the above-described comparison detection is performed, a pattern having a higher level on the detection side than the reference side is detected as a foreign substance.
In order to avoid such a situation, in the present invention, first and second level conversion circuits are provided for the multi-level conversion. As a result, the first level conversion circuit obtains the first level by converting the luminance signal (first luminance signal) for performing the foreign substance detection to the chip which is detecting the foreign substance. Adjacent A luminance signal (second luminance signal) is obtained from a position corresponding to a position where foreign matter detection is performed on the chip, and the level is converted by a second level conversion circuit to obtain a second level. Then, the first level and the second level are compared with each other. At this time, the first level conversion circuit makes the level conversion value of the first luminance signal for the pattern portion lower than the level conversion value of the reference side pattern portion. Like Performs compression conversion. The details of the compression will be described later. This prevents the pattern portion from being erroneously detected as a foreign substance.
[0012]
Therefore, in the embodiment described below, the level conversion circuit is composed of two: a pattern side level conversion circuit (first level conversion circuit) and a foreign matter side level conversion circuit (second level conversion circuit). Is done. The conversion to the multi-valued level by these is performed in eight steps in the embodiment. Further, the width of each of the eight stages of conversion of the luminance signal of the foreign substance level conversion circuit into a multi-valued level is greater than the width of each stage of the conversion of the luminance signal into a multi-valued level of the pattern side level conversion circuit. And it is set to about four times. As a result, the conversion of the luminance signal to the multi-valued level by the foreign matter side level conversion circuit is compressed to 1/4.
Note that the level conversion circuit does not necessarily need to be separated into two as described above. Simply, each luminance signal is level-converted by one level conversion circuit, and even if the multi-valued levels of the corresponding positions of the respective chips are compared with each other, the effect that the detection condition is less susceptible than in the past is obtained. can get.
[0013]
Further, as the plurality of steps for determining the level of the conversion source of the level conversion, three or more steps are preferable.
Further, the pattern-side level conversion circuit generates a level-converted reference level, which is a comparison reference for foreign substance detection. This is because the pattern is formed in the portion, and in the XY scanning method, most of the signal indicating the converted level generated by this circuit is related to the luminance signal obtained at that time from the pattern. In this regard, the foreign matter-side level conversion circuit generates a signal indicating the level obtained by level-converting the luminance signal for foreign matter detection.
[0014]
By the way, as the sensor for generating the luminance signal, in the embodiment, a one-line CCD sensor is used in which a large number of detection elements are arranged in one line to generate a luminance signal corresponding to the detection elements. Can use an optical sensor that generates a luminance signal as a detection signal corresponding to a large number of pixels, and is not limited to a one-line optical sensor.
Further, in the following embodiment, for the sake of explanation, the description will be made mainly with respect to the XY scanning type foreign matter detection device. Can be similarly applied.
[0015]
【Example】
In FIG. 1, reference numeral 50 denotes a foreign matter detection unit, which corresponds to the foreign matter detection unit 5 in FIG. The foreign matter detection unit 50 includes an A / D conversion circuit (A / D) 51, a level conversion circuit 52a (hereinafter referred to as a pattern-side conversion circuit 52a) that obtains a comparison reference level by performing level conversion on a luminance signal obtained from the pattern, A level conversion circuit 52b (hereinafter referred to as a foreign substance conversion circuit 52b) for converting the level of the luminance signal for the image signal, a line memory 53, a maximum value detection circuit 54, delay circuits 55 and 56, a foreign substance determination circuit 57, and a controller 58. .
[0016]
Further, in this embodiment, as shown in FIG. _T Are formed in a line to form a foreign substance detection area on the wafer, and an image of the linear foreign substance detection area is formed on the CCD image sensor 42a of the light receiving section 42 to perform foreign substance detection by XY scanning. Here, the CCD image sensor 42a is a long one-line sensor of about 5000 pixels. In addition, the coordinate conversion unit 62 in FIG. 4 is unnecessary because of the relationship between the XY scanning method and is omitted.
By the way, the applicant of the present invention for a technique of forming the above-mentioned linear foreign substance detection area on a wafer and detecting foreign substances by a CCD image sensor is disclosed in JP-A-9-170986 , Has applied for a “foreign matter inspection device”.
The A / D 51 receives an analog luminance signal i generated corresponding to each detection pixel from the light receiving unit 42 including the CCD image sensor 42a and the amplifier 42b, and converts the analog luminance signal i into an 8-bit 256-gradation digital value. To the pattern side conversion circuit 52a and the foreign matter side conversion circuit 52b.
[0017]
The pattern-side conversion circuit 52a and the foreign-matter-side conversion circuit 52b receive the data of the A / D 51, convert the data to one of three-bit eight-level multi-levels, and convert the data to multi-levels. 3-bit data indicating one of eight levels is generated according to the level. Here, the level conversion stage for the level of the luminance signal i is different between the pattern side conversion circuit 52a and the foreign matter side conversion circuit 52b.
The line memory 53 receives the 3-bit 8-level multilevel data of the pattern-side conversion circuit 52a and converts the level of each pixel into 55 pixels corresponding to an area of 11 × 5 pixels. The bit data is buffered, and 55 pixels of the buffered 3-bit data are sent to the maximum value detection circuit 54 in parallel.
[0018]
As a specific circuit of the line memory 53, the line memory 53 is composed of shift registers of 55 stages each provided three in parallel corresponding to three bits of multilevel data. The output of each stage of the three shift registers is sent to the maximum value detection circuit 54, respectively. The three shift registers receive the 3-bit data level-converted by the pattern-side conversion circuit 52a in parallel, one bit at a time, and shift one bit each time they are received. As a result, the oldest level conversion data is discarded, the latest data for 55 pixels (predetermined amount) is always stored, and these outputs are sent to the maximum value detection circuit 54.
The line memory 53 may be configured by a FIFO memory that stores data of 55 pixels instead of the shift register. In this case, the output data of the pattern-side conversion circuit 52a is sequentially stored in the FIFO memory, and the stored data is output to a register for 55 pixels of 3 bits provided in the maximum value detection circuit 54.
[0019]
The maximum value detection circuit 54 determines the data having the maximum value from the multi-valued data for 55 pixels of 3 bits, 56 And a large number detection circuit 540 for detecting a large value. Each of the large value detection circuits 540 digitally compares two data of the level-converted 3-bit data of the pixel A and the level-converted 3-bit data of the pixel B, and according to the comparison result of the comparator 54a. A latch circuit 54b for latching the larger of the converted data of the pixels A and B. Here, each large value detection circuit 540 is sequentially connected in a step-by-step manner in a tournament system, and detects the maximum value of a 3-bit level value of 55 pixels. That is, a large stage is detected at a certain stage, the large ones detected at the previous stage are compared at the next stage to detect a large one, and the maximum value of the level values is detected at the last stage at the last large value detection. Obtained in the latch circuit 54b of the circuit 540.
[0020]
One-chip delay circuit 55 receives 3-bit data indicating one of eight levels from foreign matter conversion circuit 52b. With reference to the pixel Ra at the center position of the 11 × 5 pixel area W (see FIG. 2) of the maximum value detecting circuit 54, the 3-bit data received by the one-chip delay circuit 55 is one bit per pixel Ra. It becomes the level conversion value of the luminance signal of the pixel S at the position shifted by the number of pixels for the chip. As shown as a test pixel S in the center of FIG. 2, the one-chip delay circuit 55 delays data for one chip time (predetermined time) corresponding to, for example, a sampling timing shift of 5000 × 5 pixels. To generate 3-bit data whose timing is delayed by one chip with respect to the pixel Ra. This becomes the multi-level data of the detection pixel S. The foreign object presence / absence determination circuit 57 receives the data converted to the multi-value level of the detection pixel S.
[0021]
Note that the reason for detecting the maximum value in the range of the area W of 11 × 5 pixels is originally that each of the inspection pixel of the chip to be inspected and the pixel located at the position corresponding to the inspection pixel of the adjacent chip. It is sufficient to compare the conversion levels of the luminance signals with each other, but it is impossible to make the positioning accuracy of the detection optical system so high. Therefore, the area W is set in consideration of the deviation of the position accuracy on the reference side from the foreign matter inspection side, and the maximum value is detected in the area W to set the conversion level of the corresponding position. Therefore, the size of the area W is not limited to the range of 11 × 5 pixels, but is determined by the detection position accuracy or the like in the detection optical system of the inspection apparatus.
[0022]
The two-chip delay circuit 56 is a circuit in which the delay of one chip of the one-chip delay circuit 55 is reduced to two chips, and its output receives 3-bit data output from the maximum value detection circuit 54. This outputs an output delayed by two chips, and sends it to the foreign matter presence / absence determination circuit 57. Therefore, this corresponds to the luminance signal of the pixel having the maximum value among the data of the area W including the pixel Rb (hereinafter referred to as reference pixel) which is a comparison reference shifted by two chips from the area W including the pixel Ra in FIG. Is output. For convenience of explanation, here, the pixel Rb at the center position corresponding to the pixel Ra is assumed to be the pixel having the maximum value. The positions of the pixels Ra and Rb are pixels at corresponding positions in an adjacent chip which is shifted by one chip with respect to the inspection pixel S.
The foreign matter presence / absence determination circuit 57 further receives the level conversion data for the pixel having the maximum value in the current 11 × 5 pixel area W directly from the maximum value detection circuit 54, but as described above, this is the reference pixel Ra. Is 3-bit data for
[0023]
As a result, the foreign object presence / absence determination circuit 57 is configured by a comparator that compares digital values. That is, when the pixel S to be inspected is received, the level-converted 3-bit data is received for each of the reference pixel Ra one chip behind and the reference pixel Rb one chip before this.
The foreign object presence / absence determination circuit 57 first compares the converted level values of the luminance signals of the reference pixels Ra and Rb and selects the larger one. Then, the selected reference pixel is compared with the 3-bit level-converted data of the inspection pixel S shifted by one chip from the reference pixel, and when the data value of the inspection pixel S is larger than the comparison data value, A detection signal indicating the presence of a foreign substance is generated, and the detection signal and detection position data including the X coordinate and the Y coordinate (the angle signal θ and the position signal R indicating the scanning position in the case of rotational scanning) are added from the controller 58 to the foreign substance data. Is generated and sent to the buffer memory 61. At this time, the foreign substance presence / absence determination circuit 57 updates the address of the buffer memory 61 each time foreign substance data is transmitted, and sequentially stores the foreign substance data at the updated address position of the buffer memory 61.
The X coordinate and the Y coordinate are sent from the control circuit 25 or the MPU 63 to the foreign substance detection unit 50. In the rotational scanning, the angle signal θ and the position signal R are similarly sent from the control circuit 25 to the foreign matter detection unit 50.
[0024]
The pattern-side conversion circuit 52a and the foreign-matter-side conversion circuit 52b are each composed of a RAM, receive A / D conversion data from the A / D 51, and use the digital value of the detected luminance signal as an address for the RAM. An access is made, and data read from the accessed address is converted to a level value. Thus, one level-converted data of three bits and eight gradations corresponding to the level of the luminance signal is obtained.
By this conversion, each luminance signal is set to one of eight levels of the pattern side P0 to P7 and the foreign matter side S0 to S7 according to the multiple levels as shown in FIG. In addition, in the conversion of the luminance signal to the multi-valued level, the width of the conversion step in each stage of the foreign matter conversion circuit 52b is larger than the width of the conversion step of the pattern side conversion circuit 52a. As a result, the luminance signal on the foreign matter side, that is, the detection signal is compressed and level-converted.
[0025]
The data stored in the RAM is stored in the controller 58 as a data conversion table. Referring to this table, the controller 58 uses the respective values of the luminance signal as the address values of the RAM, for example, and converts the 8-bit 3-bit data of the conversion levels “0” to “7” shown in FIG. Is stored. That is, the controller 58 stores in the RAM of the pattern-side conversion circuit 52a "0" as P0 at addresses 0 and 1, "1" as P1 at addresses 2 and 3, and "2" as P2 at addresses 4 and 5. "," 3 "as P3 in addresses 6 and 7," 4 "as P4 in addresses 8 to 15," 5 "as P5 in addresses 16 to 23, and" 6 "as P6 in addresses 24 to 39. , "7" is stored as P7 at addresses 40 to 64, respectively.
Similarly, the controller 58 stores “0” as S0 at addresses 0 to 7, “1” as S1 at addresses 8 to 15, and S2 at addresses 16 to 23 in the RAM of the foreign matter conversion circuit 52b. “2”, “3” as S3 in addresses 24-31, “4” as S4 in addresses 32-63, “5” as S5 in addresses 64-95, and “6” as S6 in addresses 96-159. Is stored as S7 at addresses 160 to 255, respectively. It is preferable to add an initial value C as an offset to the lowest level in the level conversion on the foreign matter side. In such a case, the last address value in the range of the level of the luminance signal may be shifted by adding C and stored.
[0026]
Next, the multilevel quantization level conversion having steps of different widths will be described with reference to FIG.
As described above, if the light receiving condition of the light receiving element fluctuates, or the optical detection condition fluctuates or differs, the detection level changes for the same pattern and a detection error occurs. However, between the adjacent chips on the same wafer, the light receiving condition and the detection condition are often affected to the same degree. Therefore, comparing the level of the other luminance signal with reference to the light receiving condition and the detecting condition, The influence on the fluctuation of the detection condition is relatively suppressed. Furthermore, if the level of the luminance signal is converted in multiple stages, even if the converted value fluctuates in accordance with the light receiving condition or the inspection condition, the luminance signal of the chip on the foreign matter detection side and the adjacent signal serving as a reference for comparison with the luminance signal are compared. Since the luminance signal of the chip to be processed undergoes the same fluctuation, there is almost no fluctuation in the relative value of the converted value as a comparison condition.
[0027]
If this concept is adopted, the pattern part is compared with the pattern part and the part other than the pattern is compared with the part other than the pattern, so that there is no need to distinguish the pattern part from the rest. However, even if such a concept is adopted, in the comparison at the same position of the adjacent chip, the level of the luminance signal on the reference side decreases, while the level of the luminance signal on the pattern portion on the detection side increases. The level of the luminance signal on the detection side may exceed the level of the luminance signal on the reference side. In such a case, erroneous detection of a foreign substance occurs.
By the way, according to the results of experiments on a large number of wafers, the level of the luminance signal with respect to the foreign matter indicates that the foreign matter on the pattern or the foreign matter riding on a place other than the pattern has the foreign matter on each. The average value of the peak level of the luminance signal is about four times or more higher than that of the non-riding one. However, this is much lower for a luminance signal with a low detection level. If the accuracy of the detection optical system is improved, the magnification will be slightly different from the above.
[0028]
According to the above experimental results, if the foreign substance is detected based on a luminance signal having a high detection level with a magnification of 4 times as a reference, the luminance signal on the foreign substance detection side is compressed to 1/4, and the magnitude is compared with the reference side. Can detect foreign matter.
That is, since the level of the luminance signal when foreign matter is on the pattern is four times or more on average, even if the level is compressed to １ ／ and the level is converted by the foreign matter detection side level conversion circuit 52b, The conversion level is in a range exceeding the conversion level for the luminance signal in the adjacent chip by the pattern-side level conversion circuit 52a. Therefore, foreign matter can be detected based on a high-level luminance signal.
By compressing the luminance signal on the detection side in this way, it is possible to reduce the conversion level of the pattern portion where no foreign matter is on the detection side. With the exception of some luminance levels being high, even if the conversion level of the pattern on the reference side is low, the conversion level value of the pattern portion on the detection side can be suppressed to a value lower than this. Therefore, the erroneous detection of the foreign matter can be suppressed.
[0029]
For this reason, as an embodiment, the detection level for the luminance signal is compressed to 1/4. Therefore, the level conversion width on the foreign matter detection side is quadrupled. FIG. 3 shows such a multi-stage level conversion. The luminance signal L1 is a luminance signal other than the pattern. The luminance signal L2 is the luminance signal of the pattern portion, and the luminance signals when foreign substances are on these are LS1 and LS2, respectively.
As a specific conversion width, in FIG. 3, for example, 64 gradations (= 256/4) of ８ of the 8-bit 256 gradations are set within the range of the level of the luminance signal on the pattern side where no foreign substance is placed. And divide it into eight stages. Therefore, the pattern is divided into eight stages on the pattern side (P side) from P7 = 40 to 64, P6 = 24 to less than 40, P5 = 16 to less than 24, P4 = 8 to less than 16 and P3 = 6. More than or equal to less than 8, P2 = 4 or more to less than 6, P1 = 2 or more to less than 4, and P0 = 0 to less than 2.
[0030]
On the other hand, in the level conversion of eight steps on the foreign matter side (S side), S7 to S0 are S = n × P, n = 4, S7 = 4 × P7 = 160 or more to 255, and S6 = S5 = 60 or more to less than 96, S4 = 32 or more to less than 64, S3 = 24 to less than 32, S2 = 16 to less than 24, S1 = 8 Above, it is less than 16 and S0 = 0 to less than 8.
The respective data stored in the RAM for the level conversion correspond to the above numerical values.
When the conversion level on the foreign substance side (S side in the figure) is determined from the conversion side on the pattern side (P side in the figure), the conversion level on the pattern side is not limited to n = 4. In the level conversion on the S side, compression may be performed to reduce the level of the luminance signal on the foreign matter side to the extent that the pattern is not erroneously detected as a foreign matter. In particular, when detecting foreign matter in a lower level luminance signal, n takes a value greater than 1 and 4 or less.
[0031]
Generally, the width of each stage of the multi-level level conversion for the luminance signal of the foreign substance side level conversion circuit 52b is determined by the average value of the luminance signal when the foreign substance is loaded and the average value of the luminance signal when the foreign substance is not loaded. Is n, the width of each stage in the conversion stage of the foreign substance level conversion circuit 52b to the multi-valued level is equal to the width of each stage in the conversion stage to the multi-valued level of the pattern side level conversion circuit 52a. It suffices that it be m times (1 <m <n).
Further, each data for compressing and converting the level of the luminance signal may be obtained as an experimental value. When calculating the step width of the level conversion as the experimental value, for example, the equation of S = P + k + C is adopted according to the experimental value, and the value of k is gradually increased as the level increases. Further, with respect to P0, the range may be set to 0 to less than k + C with C being the initial value, and the range may be shifted by the initial value by adding the initial value C to the value of each stage.
[0032]
The data obtained by such an equation is stored in the data conversion table of the controller 58. The data in this table is set as data in the internal memory of the controller 58 under the control of the microprocessor (MPU) 63 of the data processing unit 6. In this way, the data value can be arbitrarily set from the outside under the control of the microprocessor 63.
As a result, each level is converted into one of eight gradations by multi-leveling in eight stages according to FIG. Note that the comparison criterion is the maximum value in the predetermined area, but this may be the data Ra and Rb of the pixel at the position corresponding to the inspection pixel.
[0033]
By the way, in the embodiment, the luminance signal from the inspection area in the inspection chip and the luminance signal from the adjacent chip are generated by delaying the same luminance signal by the delay circuit. In this case, for example, the position of the one-chip delay circuit 55 is moved between the A / D 51 and the foreign substance side level conversion circuit 52b, and the foreign substance side level conversion circuit 52b and the pattern side level conversion circuit 52a are respectively moved from the foreign substance inspection area. And a luminance signal from an adjacent chip may be received. Further, the position of the one-chip delay circuit 55 may be moved to the output of the maximum value detection circuit 54 so as to be in parallel with the two-chip delay circuit 56.
[0034]
【The invention's effect】
As described above, in the present invention, the detection signal (luminance signal) is multi-valued in a plurality of predetermined steps, and the multi-value level obtained by this is multi-valued at a similar position of an adjacent chip. And compare it to the level. As a result, even if the detection conditions change, the stages at which both are multivalued change in accordance with the change, respectively, so that the comparison of these multivalue levels is a relative comparison. Therefore, even if the light receiving conditions of the light receiving element fluctuate, or the optical detection conditions fluctuate or differ, a foreign matter detection error hardly occurs.
As a result, a patterned wafer foreign matter inspection device capable of detecting foreign matter with higher precision can be realized.
[Brief description of the drawings]
FIG. 1 is a block diagram centering on a foreign substance detection unit in one embodiment of a patterned wafer foreign substance inspection apparatus of the present invention.
FIG. 2 is an explanatory diagram of the inspection state.
FIG. 3 is an explanatory diagram of the level conversion to the multilevel level.
FIGS. 4A and 4B are views showing an example of a rotary scanning type foreign matter inspection apparatus, in which FIG. 4A is an overall configuration diagram, and FIG. FIG. 3C is an explanatory diagram of a pattern and foreign matter in each chip.
FIG. 5 is an explanatory diagram of distribution characteristics of scattered light of a pattern.
FIG. 6 is a waveform diagram showing an example of a detection signal for a luminance signal and a foreign substance.
[Explanation of symbols]
1 ... wafer with pattern to be inspected, 1 '... test wafer,
11 IC chip, 2 rotating mechanism, 21 rotating stage,
22: motor (M), 23: XY moving mechanism,
24: rotary encoder, 25: control circuit,
3. Projection unit, 31A, 31B laser light source, 32A, 32B focusing lens,
4 light receiving section, 41 light collecting lens, 42 light receiving section,
5, 50 ... foreign substance detection unit, 51: A / D conversion circuit (A / D),
52a... Reference level conversion circuit on the pattern side (level conversion circuit on the pattern side);
52b: level conversion circuit on the foreign matter detection side (foreign matter level conversion circuit);
53 ... Line memory,
54: maximum value detection circuit, 55, 56 ... delay circuit,
57: foreign matter presence / absence determination circuit, 58: controller,
6 data processing unit, 61 buffer memory, 62 coordinate conversion unit
63 ... Microprocessor (MPU)
7 ... output unit,
L _T ... Laser beam, S _P … Laser spot,
PT ... pattern, Q, Q ₁ , Q ₂ ... foreign matter,
L _R ... scattered light, L _RP … Pattern scattered light, L _RQ ... scattered light of foreign matter,
i: luminance of scattered light, Δi: step luminance, i: luminance signal,
R: scanning position of spot,
θ: wafer rotation angle, Δθ: step angle, θ: angle signal,
θp: specific angle, V ₁ , V ₂ ... Fixed threshold.

Claims (3)

A pattern-formed wafer having a pattern formed as an IC chip is irradiated with a laser beam at a predetermined angle to receive the scattered light, obtain a detection signal corresponding to the level of the received light, and respond to the detection signal. A level conversion circuit for converting the level of the detection signal in a certain chip into one of a plurality of multilevel levels, and a signal indicating the level converted by the level conversion circuit. And determining whether or not there is a foreign object by comparing the detection signal at a similar position of a chip adjacent to the certain chip with a signal indicating a converted level obtained by converting the detection signal by the level conversion circuit. and a circuit, the predetermined range is set for the same position of the adjoining chips were the conversion in the adjacent chips Signal indicating the bell, the foreign matter inspection apparatus for patterned wafer wherein a maximum value selected from a predetermined range. A CCD optical sensor having detection elements corresponding to a large number of pixels arranged in a line; and an A / D conversion circuit for A / D converting a signal detected by the detection element, wherein the detection signal is An output of an A / D conversion circuit, wherein the plurality of stages are three steps or more, the level conversion circuit has first and second level conversion circuits receiving the detection signal, The width of each stage of multi-level conversion of the detection signal by the level conversion circuit is larger than the width of each stage of multi-level conversion of the detection signal by the second level conversion circuit, and the first level conversion is performed. An output of a circuit is assigned to a signal indicating the converted level in the certain chip, and an output of the second level conversion circuit is assigned to a signal indicating the converted level in the adjacent chip. Terra is to have claim 1 foreign matter inspection apparatus for patterned wafer according. The width of each stage of the multi-level level conversion for the detection signal of the second level conversion circuit is a ratio between the average value of the detection signal when the foreign substance is loaded and the average value of the detection signal when the foreign substance is not loaded. Is n, the width of each stage in the stage of converting the first level conversion circuit to a multi-level is smaller than the width of each stage in the stage of converting the second level converter to the multi-level. 3. The apparatus for inspecting foreign matter of a patterned wafer according to claim 2, wherein the number is m times (where 1 <m <n).

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