Patent Application
20110141598
The present invention relates to a disk surface defect inspection method and apparatus. More particularly, the present invention relates to a disk surface defect inspection method and apparatus for detecting surface defects on a magnetic disk, or on a glass substrate of the magnetic disk, by a quick process for determining whether the detected defects form an annular scratch defect, an island defect, or other defects, and for classifying the defect shape.
There have been used optical measurement techniques to detect surface defects on a disk such as a magnetic disk or a semiconductor substrate. For example, JP-A No. 89336/1987 discloses a technique for inspecting foreign matters or pattern defects by irradiating a laser beam on a semiconductor substrate. If a foreign matter is present on the semiconductor substrate, the scattered light from the foreign matter is detected and compared to the last detection result of the semiconductor substrate of the same type. This is publicly known to those skilled in the art.
Further, U.S. Pat. No. 5,471,298 discloses a measurement technique for measuring the size of particles (or crystal defects) of an inspection sample, by irradiating a laser beam on the inspection sample, receiving the scattered light from the particles (or the crystal defects) of the inspection sample, and converting the received light into an image.
Furthermore, as described in JP-A No. 66263/2001, there is known a disk surface defect inspection apparatus that can detect defects by irradiating a laser beam on an inspection area of a disk, and receiving the scattered light from the inspection area. Further, a dedicated light receiving element is provided for annular scratch defect detection. Thus, the apparatus selectively detects an annular scratch defect and determines the continuity of the defect in the annular scratch defect detection.
Still further, JP-A No. 66263/2001 discloses a disk surface defect inspection method or apparatus using a process program to recognize each defect shape by determining the continuity of defects in both radial and circumferential directions. Then, the detected defects are grouped into a single defect to determine and classify the defect shape.
In the defect inspection of a recording medium used in computer systems, such as a magnetic disk or a glass substrate of the magnetic disk, there is an increase in the detection sensitivity due to the recent development of the high density recording media. The increase in the detection sensitivity increases the number of detected defects while reducing the size of the defects. This leads to a problem that the process load on a data processor used for grouping defects increases, requiring a lot of time for the inspection.
There is also a problem with the detected defects having a very small size. In this case, the data processing using the light receiving element specific to the annular scratch defect as described in Patent Document 3, even adds an extra process. This leads to an increase in the process load by the additional process.
The present invention addresses the problems of the prior art, and aims to provide a disk surface defect inspection method and apparatus capable of detecting surface defects on a magnetic disk by a quick process for determining whether the defects form a circumferential scratch, namely, an annular scratch defect, or an island defect.
The present invention also aims to provide a disk surface defect inspection method and apparatus capable of detecting surface defects on a magnetic disk, by a quick process for determining whether the defects form an annular scratch defect, an island defect, or other defects, and for classifying a defect shape.
In other words, the disk surface defect inspection method and apparatus according to the present invention includes: a defect data acquisition step for inspecting an entire surface of a disk to detect defects, and acquiring data of the detected defects together with position coordinates on the disk; a radial histogram generation step for dividing the entire surface of the disk into a large number of areas at a predetermined width in a radial direction of the disk, to set a large number of sum tracks to calculate the total number of the defects, and generating histogram data containing the number of defects in each of the large number of sum tracks in radius, with the number of defects in each sum track as a frequency; or an angular histogram generation step for dividing the entire surface of the disk into a large number of angles at a predetermined equal angle in a circumferential direction of the disk, to set a large number of sum angle areas to calculate the total number of the defects, and generating histogram data containing the number of defects in each of the large number of sum angle areas in angle, with the number of defects in each sum angle area as a frequency; a step for calculating the standard deviation of the histogram data containing the number of defects detected in the sum tracks in radius, and calculating the standard deviation of the histogram data containing the number of defects detected in the sum angle area in angle; and a defect inspection step for detecting an annular scratch defect in the histogram data containing the number of defects in radius, with respect to each sum track with a deviation higher than the standard deviation of the particular histogram data, or for detecting'an island defect in the histogram data containing the number of defects in angle, with respect to each sum angle area with a deviation higher than the standard deviation of the particular histogram data.
According to the present invention, it is possible to detect an annular scratch defect in sum tracks with a deviation exceeding the standard deviation of an amount of defects detected (the number of defects detected) in radius, in the histogram data containing the number of defects in radius (hereinafter referred to as the radial histogram). It is also possible to detect an island defect in sum angle areas with a deviation exceeding the standard deviation of an amount of defects detected in angle, in the histogram data containing the number of defects in angle (hereinafter referred to as the angular histogram). In this way, the defect detection process can be performed step by step, by separating the annular scratch defect or the island defect from the other defects. As a result, a process load on the data processor can be reduced even if the number of detected defects increases.
In this case, the annular scratch defect is determined based on the standard deviation of the radial histogram. This is because the annular scratch defect is on a circumference in a certain radius range. In other words, when an annular scratch defect is present in a certain radius range, the number of defects detected in the sum track area of the particular radius range is significantly larger than the standard deviation of the radial histogram. Also the island defect is determined based on the standard deviation of the angular histogram. This is because an island defect is included in a certain sum angle area of the disk that is divided into equal angles in the circumferential direction. In other words, when an island defect is present in a certain sum angle area, the number of defects detected in the particular sum angle area is significantly larger than the standard deviation of the angular histogram.
As described above, the annular scratch defect determination and the island defect determination can be classified according to the standard deviations of the radial and angular histograms. Thus, it is possible to determine each determination target and perform the defect determination. In addition, the amount of process data of the determination target can be reduced in each determination of the shape of the defects forming annular scratch defect or island defect. Thus, the process load on the data processor for defect detection is reduced. After such a step-by-step process, the process proceeds to the next step of detecting the shape and the like of the remaining defects other than the annular scratch defect and the island defect. For this reason, the amount of data to be processed in the detection process is further reduced.
As a result, the present invention allows for a quick process in the disk surface defect inspection method and apparatus, to determine whether the defects are an annular scratch defect, an island defect, or other defects, or to classify the defect shapes.
It is to be noted that when the target disk is discrete track media (DTM), the number of defects is large, so that the advantage of the quick process of the defect inspection is particularly significant.
These features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.
In
The R·θ stage 3 includes an R encoder 9a for generating a distance pulse corresponding to the distance of the spindle 2 in the disk radial direction (R direction). The spindle 2 includes a θ encoder 9b for generating an angle pulse corresponding to a rotation angle θ of the disk 1.
Reference numeral 4 denotes a laser light source. A laser beam L from the laser light source 4 is irradiated onto and reflected from an inspection area S of the disk 1. The reflected light is input to a sensor (detector) 5 including a light receiving element, or photodiode, such as APD or CCD.
The light reception signal generated in the sensor 5 is amplified by an amplifier 6, and added to an A/D conversion circuit (A/D) 8 through a band-pass filter (BPF) 7. In the A/D 8, the level (voltage) of the light reception signal is converted to a digital value. Then, the digitally converted light reception signal (hereinafter the light reception signal) is compared to a predetermined threshold (threshold level) in a defect determination circuit 13, to determine whether the value of the light reception signal exceeds a predetermined threshold.
When the value of the light reception signal exceeds the threshold, it is determined to be a defect. In this case, the defect determination circuit 13 outputs a bit pulse, or a defect bit, to a defect memory 14 as a defect detection signal. For example, defect bit 1 shows presence of a defect while defect bit 0 shows absence of a defect.
The A/D 8 and the defect memory 14 are supplied with a clock CLK from a sampling clock generating circuit 12, respectively. In response to the clock CLK, the level of the light reception signal is converted to a digital value by the A/D 8. Also, in response to the clock CLK, the determination data result (defect bit) of the light reception signal is stored in the defect memory 14, together with the position data POS (the data of the coordinate position of the defect on the disk).
In other words, when the defect bit is “1”, which shows the presence of a defect, the position data POS of the coordinates of the defect at this time is written to the defect memory 14 according to the defect bit. In this way, the position data POS is sequentially stored in a predetermined area of the defect memory 14.
In this case, only the position data POS may be stored in the defect memory 14. It is also possible that the light reception level of the light reception signal at the defect position is stored, together with the defect bit in addition to the position data POS. In
The position data POS, which is input to the defect memory 14, is the data of the coordinates corresponding to the current scan position of the laser beam L. The position data POS is input to the defect memory 14 from the R·θ coordinate position generating circuit 11, in the form of the coordinates (the position of the defect detected) on the disk in two dimensions R, θ of the inspection area S of the disk 1 to which the laser beam L is irradiated.
The R·θ coordinate position generating circuit 11 receives an angle pulse indicating the rotation amount in the θ direction, from the θ encoder 9b. The R·θ coordinate position generating circuit 11 also receives a distance pulse indicating the distance in the R direction, from the R encoder 9a. Then, the R·θ coordinate position generating circuit 11 generates the coordinates (R, θ) as data.
Reference symbol Cu denotes an annular scratch defect, reference symbol Id denotes an island defect, and reference symbol F denotes other defects.
As shown in
In the sum tracks Tl to Tn and the sum angle areas θl to θm, it is assumed that the annular scratch defect Cu is present on the sum track Ti, and that the island defect Id is present in the sum angle areas θi and θi+1.
Here, consideration will be given to the relationship between the annular scratch defect Cu and the sum tracks Tl to Tn in
Next, consideration will be given to the relationship between the island defect Id and the sum angle areas θl to θm in
As described above, when a radial histogram is calculated from the detected defects, it is shown that the number of defects in the sum track with the annular scratch defect Cu is much larger than the standard deviation of the histogram. Similarly, when an angular histogram is calculated from the detected defects, it is shown that the number of defects in the sum angle area with the island defect Id is much larger than the standard deviation of the histogram.
The deviation of the radial histogram is related to the annular scratch defect. This is because the annular scratch defect is on a circumference of an annular of a predetermined radius. Further, the deviation of the angular histogram is related to the island defect. This is because the island defect is included in about one or two angle areas of the disk divided into equal angles in the circumferential direction. However, when the division angle is reduced, the number of angle areas in which the island defect is included is slightly increased.
Here, the track width is set to a predetermined radius range in which an annular scratch defect occurs. For example, the disk 1, or DTM is divided into a large number of sum tracks at a predetermined width in the range of radial widths from 5 μm to 10 μm in the radial direction of the DTM. Then, the total number of defects in each of the sum tracks is calculated to generate data of the radial histogram. It is preferable that the width of the sum tracks is in the range of 5 μm to 10 μm, because in most cases the common annular scratch defect occurs in one sum track, or in three sum tracks (middle and two adjacent sum tracks).
Similarly, in the case of the island defect in the DTM, the disk is divided into equal angles in the circumferential direction, to set a large number of fan-shaped sum angle areas with a predetermined angle in the range of 0.5° to 3°. Then, the total number of defects in each of the sum angle areas is calculated to generate data of the angular histogram. It is preferable that the angle of the sum angle areas is in the range of 0.5° to 3°, because in most cases the common island defect occurs in one sum angle area, or in three sum angle areas (middle and two adjacent sum angle areas).
Hereinafter, a description will be given of the step-by-step process for performing the annular scratch defect determination and the island defect determination, to determine the defect shape by referring to the standard deviations.
Returning to
The memory 17 stores a defect detection program 17a, a radial/angular histogram generation program 17b, a radial/angular deviation calculation program 17c, a defect shape determination program 17d, a continuity judgment program 17e, a defect size classification program 17f, and a helical scan program 17g or other programs. The memory 17 also includes an operation area 17h.
Further, various data files and the like are stored in an external storage device 21, such as a hard disk device (HDD), connected to the data processor 15 through the interface 19.
The defect detection program 17a is executed by the MPU 16. The MPU 16 first calls and executes the helical scan program 17g based on the defect detection program 17a. Then, the MPU 16 controls the R·θ stage 3 under the helical scan program 17g to helically scan the disk 1, and acquires defect data of the entire surface of the disk 1, as well as the R·θ coordinates of the defects. Then, the MPU 16 controls to store the acquired data in the defect memory 14. Next, the MPU 16 controls to receive the defect data of the entire surface of the disk 1 from the defect memory 14 through the interface 19. Then, the MPU 16 controls to store the received defect data in the operation area 17h of the memory 17. In this way, the defect data (DALL) of the entire surface of the disk 1 is acquired and stored in the operation area 17h (step 101).
After the above step, the MPU 16 calls and executes the radial/angular histogram generation program 17b.
The radial/angular histogram generation program 17b is executed by the MPU 16. Based on this program, the MPU 16 sets the sum tracks Tl to Tn (see
Next, the MPU 16 divides the disk 1 into equal angles in the circumferential direction at an equal angle of 1°, to set the fan-shaped sum angle areas θl to θm (see
Next, the MPU 16 calls and executes the radial/angular deviation calculation program 17c. The radial/angular deviation calculation program 17c is executed in the following steps. First the MPU 16 calculates the standard deviation σr of the radial histogram stored in the operation area 17h. In addition, the MPU 16 calculates deviations of the individual sum tracks. Then, the MPU 16 stores the results in the memory (operation area 17h). Further, the MPU 16 calculates the standard deviation σt of the angular histogram stored in the operation area 17h. In addition, the MPU 16 calculates deviations of the individual sum angle areas. Then, the MPU 16 stores the results in the memory (operation area 17h) (step 104).
Next, the MPU 16 judges whether the standard deviation σr is less than 1 (step 105). When the standard deviation σr is less than 1, it is judged as YES in step 105, assuming there is no annular scratch defect. Then, the MPU 16 judges whether the standard deviation σt is less than 1 in step 106a. When the standard deviation σt is less than 1, it is judged as YES in step 106a, assuming there is no island defect. The MPU 16 switches to a process of step 110 to detect other defects.
If NO in step 106a, the MPU 16 switches to a process of island defect detection in step 109.
When the standard deviation σr is 1 or more in the judgment in step 105, it is judged as NO in step 105. Then, the MPU 16 judges whether the standard deviation σt is less than 1 in step 106. When the standard deviation σt is less than 1, it is judged as YES in step 106, assuming there is no island defect. The MPU 16 moves to a process of annular scratch defect detection in step 109a. When the standard deviation σt is 1 or more, it is judged as NO in step 106. Next, the MPU 16 calls and executes the defect shape determination program 17d.
Here, the defect shape determination program 17d is executed by the MPU 16. Based on this program, the MPU 16 classifies the defect detection into annular scratch defect detection, island defect detection, and other defect detection. Then, the MPU 16 performs the defect detection process by referring to the standard deviations 94 r and σt with respect to the defect data of the disk 1 stored in the operation area 17h.
More specifically, the MPU 16 first compares the standard deviations σr and σt, and judges whether σr is larger than σt (step 107). In this way, the MPU 16 judges the larger one among the two standard deviations, and performs the annular scratch defect detection process or the island defect detection process according to the judgment result. It is to be noted that the annular scratch defect detection process includes the case in which the two standard deviations are equal to each other.
As a result of the judgment in step 107, when the standard deviation σr of the radial histogram is larger than or equal to the standard deviation σt of the angular histogram, the MPU 16 first performs the annular scratch defect detection process (step 108). In this case, the MPU 16 sequentially detects an annular scratch defect in each of the sum tracks, starting from the sum track with the largest deviation of the deviations calculated in step 104 with respect to the standard deviation σr calculated from the radial histogram, to the sum track with the standard deviation σr.
At this time, the MPU 16 calls and executes the continuity judgment program 17e to perform the annular scratch defect detection. When a predetermined number, for example, 100 or more continuous defects (see
As described above, the defects are determined as a annular scratch defect. Then, a series of defect coordinates is registered as the single annular scratch defect in the operation area 17h. At the same time, the defects of the annular scratch defect are deleted from the defect data (DALL) that have been acquired and stored in the operation area 17h.
Note that in the above case, the defects are assumed to be continued by ignoring about 1 to 10 missing defects. The number of missing defects is determined depending on the sensitivity of defect detection of the apparatus. In other words, the higher the detection sensitivity, the smaller the number of missing defects.
At the time when the detection reaches the track corresponding to the standard deviation σr in the radial histogram, the MPU 16 ends the annular scratch defect detection process, and switches to the next step of the island defect detection (step 109).
Next, the MPU 16 enters the island defect detection process (step 109). The MPU 16 detects an island defect in each of the sum angle areas, starting from the sum angle area with the largest deviation of the deviations calculated in step 104 with respect to the standard deviation σt calculated from the angular histogram, to the sum angle area with the standard deviation σt. Also in the case of the island defect detection, the MPU 16 calls and executes the continuity detection program 17e to perform the detection process. The island defect is detected by grouping a predetermined number of continuous defects, and judging an island defect among the grouped continuous defects when the number of defects is, for example, 100 or more (see
Next, the MPU 16 performs the defect determination of detecting other defects with respect to the remaining defect data (DALL) (step 110). Other defects include on-line defect, isolated defect of a plurality of continuous defects, or other shape defects.
In the other defect detection, the MPU 16 calls the continuity judgment program 17e to perform a continuity judgment process with respect to all of the remaining defect data stored in the operation area 17h. The process includes the following steps: searching a defect among the remaining acquired defect data (DALL) which has a center coordinate data in the range of the diameter of the laser beam spot L from a center coordinate of a defect of interest which is selected from the remaining acquired defect data (DALL); when such defect is found as a result of the search, grouping the defects into a single defect; further searching for other data using the coordinate of the grouped defect data as new center coordinate, in the radial direction and also in the circumferential direction; grouping the defects found as a result of the search into a single defect; and registering each of the defects in the operation area 17h as a single defect occurring in a continuous range.
As a result of the determination in step 107, when the standard deviation σt of the angular histogram is larger than the standard deviation σr of the radial histogram, the island defect detection is first performed, followed by the annular scratch defect detection. In other words, contrary to the process described above, the island defect detection process (step 108a) is operated at first, and then the annular scratch defect detection process described above is operated (step 109a). Finally, the other defect judgment process (step 110) is performed.
It is to be noted that, in this case, when the standard deviations σr and σt are equal to each other, the process flow from step 108a to step 109a may be selected.
The annular scratch defect detection process of step 108 in
In
It is to be noted that each of the processes here is a subroutine process of the annular scratch defect detection or the island defect detection, which is continued from the main routine of the process of
Next, the MPU 16 judges whether the number of defects in each sum track is 6 σr or more (step 202). If NO in step 202, the MPU 16 updates the sum track (step 203), and returns to step 202. When there is no track left to be updated, the MPU 16 ends the process here, and returns to the main routine of
If YES in the judgment in step 202, the MPU 16 extracts continuous defects in each sum track with a deviation of 6 σr or more, which is at least 6 times the standard deviation of the radial histogram, from the acquired defect data (DALL), as an annular scratch defect (Dr) when the number of the defects exceeds 6 σr, namely, 6 times the standard deviation σr. Then, the MPU 16 sequentially registers the extracted continuous defects, as the annular scratch defect, in the operation area 17h (step 204). Then, from DALL=DALL−Dr, the MPU 16 deletes the annular scratch defect data (Dr) from the original defect data (DALL) (step 205).
If there is no annular scratch defect (Dr), the MPU 16 determines Dr=0, and switches to the next step. It is also possible to detect the annular scratch defect (Dr) with the number of defects being 5 σr or more, instead of 6 σr as described above.
Next, the MPU 16 calculates a standard deviation σri with respect to the new defect data (DALL=DALL−Dr) (step 206). Then, the MPU 16 judges whether the previously calculated standard deviation σr(i−1)−σri=0 is established (step 207).
If the annular scratch defect (Dr) with the number of defects being 6 σr (or 5 σr) or more is not detected in step 204, the result is Dr=0. In this case, the difference between the standard deviation σr(i−1) and the standard deviation σri is “0”.
If NO in the above judgment, the MPU 16 returns to step 204. If YES in the judgment, the MPU 16 returns to step 203 and updates the sum track.
In this embodiment, 5 σr or 6 σr or more continuous defects are extracted as the annular scratch defect (Dr) in each sum track. Because the experience shows that in most of the annular scratch defects causing a problem in the DTM, as shown in
The island defect detection process of step 108a in
In
Next, the MPU 16 judges whether the number of defects in each sum angle area is 6 σt or more (step 302). If NO in step 302, the MPU 16 updates the sum angle area (step 303), and returns to step 302. When there is no sum angle area left to be updated, the MPU 16 ends the process here, and returns to the main routine shown in
If YES in the judgment in step 302, the MPU 16 extracts continuous defects in each sum angle area with a deviation of 6 σt or more, which is at least 6 times the standard deviation of the angular histogram, from the acquired defect data (DALL), as an island defect (Dt) when the number of the defects exceeds 6 σt, namely, 6 times the standard deviation σt. Then, the MPU 16 sequentially registers the extracted continuous defects, as the island defect (Dt), in the operation area 17h (step 304). Then, from DALL=DALL−Dt, the MPU 16 deletes the island defect data (Dt) from the original defect data (DALL) (step 305).
If there is no island defect (Dt), the MPU 16 determines Dt=0, and switches to the next step. It is also possible to detect the island defect (Dt) with the number of defects exceeding 5 σt, instead of 6 σr as described above.
Then, the MPU 16 calculates a standard deviation σti with respect to the new defect data (DALL=DALL−Dt) (step 304). Then, the MPU 16 judges whether the previously calculated standard deviation σt(i−1)−σti=0 is established (step 305).
If there is no island defect (Dt) with the number of defects exceeding 6 σt (or 5 σt) detected in step 304, the result is Dt=0. In this case, the difference between the standard deviation σt(i−1) and the standard deviation σti is “0”.
If NO in the judgment of step 305, the MPU 16 returns to step 304. If YES in the judgment of step 305, the MPU 16 returns to step 303 and updates the sum angle area.
In this embodiment, 5 σt or 6 σt or more continuous defects are extracted as the island defect (Dt) in the angular histogram. Because the experience shows that in most of the island defects causing a problem in the DTM, the number of defects exceeds 5 σt in the distribution of the number of defects on the angular histogram. Thus, the island defect can be distinguished from the annular scratch defect by 5 σt.
When the island defect detection process of
In this embodiment, the deviation of the sum track for detecting the annular scratch defect is set to 6 times the standard deviation, or the deviation of the sum angle area for detecting the island defect is set to 6 times the standard deviation. However, it is possible to set the deviation to at least 3 times (3 σ) the standard deviation. Further, the number of continuous defects detected may be different in the annular scratch defect detection process and in the island defect detection process.
When the process of
Note that when the position data POS is stored in the defect memory 14 in addition to the received light levels of reception signals from the defect positions, it is possible to obtain the received light level of the signal of each defect corresponding to the position at which the defect occurs. Further, with respect to the detection signal with only one peak indicating an isolated defect, when the voltage level of the signal exceeds a threshold, the defect determination circuit 13 classifies the voltage level into one of the 5 stages (extra large, large, medium, small, extra small) according to the classification criteria. In this way, each defect can be classified and stored according to the position at which the defect occurs.
As described above, this embodiment is designed to first perform the annular scratch defect detection process or island defect detection process with the larger standard deviation, to determine the annular scratch defect or the island defect. However, the present invention is not limited to the above embodiment, and it is also possible to first perform the detection process with the smaller standard deviation to determine the annular scratch defect or the island defect.
The above embodiment exemplifies the laser beam as the irradiation light irradiated on the inspection area S of the disk 1. In this case, it is preferable to use a laser beam of an S polarization. However, the present invention is not limited to the case in which the irradiation light is the laser beam. It goes without saying that the irradiation light may be white light.
Further, the above embodiment has been described focusing on the apparatus for inspecting surface defects of a magnetic disk. However, the inspection target according to the present invention is not limited to the magnetic disk, and any other disk-shaped substrates (disks) such as wafer and CD may also be used.
Still further, although the above embodiment uses the R·θ helical scan as the scan of the disk, the present invention is not limited to such a helical scan. It goes without saying that an XY two-dimensional scan may also be used.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-282530 | Dec 2009 | JP | national |
