Automatic identification method for COP and processing defects of polished monocrystalline silicon wafer

Abstract

The invention relates to an automatic identification method for COP (coefficient of performance) and processing defects of a polished monocrystalline silicon wafer, which belongs to the technical field of Czochralski silicon single crystal and comprises the following operation steps of: 1, equally dividing a silicon wafer into 12 fan-shaped areas with angles of 30 degrees; 2, the silicon wafer is divided into three annular areas with the radius of zone 1 being 0-50 mm, the radius of zone 2 being 50-100 mm and the radius of zone 3 being 100-150 mm, and the silicon wafer is divided into three annular areas with the radius of zone 1 being 0-50 mm, the radius of zone 2 being 50-100 mm and the radius of zone 3 being 100-150 mm; thirdly, defining coordinate boundaries of all the areas according to the division modes of the first step and the second step. And 4, according to a coordinate file of particle detection, all Defects are attributed to each area. And a fifth step of counting the number of the Defects in each area. And 6, removing the maximum value and the minimum value of the number of the Defect in each area, and then respectively calculating the mean value and the standard deviation of Zone1, Zone2 and Zone3. 7, judging the standard that a certain Zone is in a COP mode as a standard deviation / mean value lt; and 0.20, on the contrary, the defect is the processing defect. The problems that failure modes are difficult to recognize and products are improperly disposed in actual production are solved.

Description

Technical Field

[0001] The invention relates to the technical field of CZ silicon single crystals, and in particular to an automatic identification method for COP and processing defects of a single crystal silicon polishing sheet. Background Art

[0002] There are three main types of defects on the surface of semiconductor silicon single crystal polished wafers: (1) Crystal Original Pit (COP); (2) Polishing Induced Defect (PID); (3) Particles. These three types of defects are collectively referred to as LLS (Laser Local Scattering).

[0003] When the number of LLS exceeds the specification, two types of disposal measures are involved: (1) downgrading or scrapping; (2) re-polishing or re-cleaning. Failure caused by COP requires downgrading or scrapping (COP defects exist on the surface and body of the silicon wafer and cannot be improved by re-polishing or re-cleaning).

[0004] Defects caused by PID need to be returned for treatment; defects caused by particles need to be returned for treatment. The difficulty encountered in actual production is that it is difficult for on-site operators to identify the LLS failure mode of silicon wafers, and improper treatment often occurs due to misidentification.

[0005] The COP patterns of polished silicon wafers can be divided into the following four types: (1) centrally concentrated; (2) symmetrically distributed on the outer ring; (3) both centrally concentrated and symmetrically distributed on the outer ring; and (4) fully distributed. Whether COP appears on the surface of the silicon wafer and what type of COP appears depends on the crystal pulling conditions at the position of the silicon wafer in the crystal ingot, which include the pulling speed and the thermal field.

[0006] Regardless of the COP mode, they all have a common feature: the distribution of COP is centrally symmetrical around the center of the silicon wafer, which is determined by the growth method of the Czochralski silicon single crystal (axisymmetric thermal field distribution and rotational pulling growth method). However, the defects and particles caused by silicon wafer processing are randomly distributed and do not have the centrally symmetrical distribution characteristics.

[0007] Patents CN101460665A, JP5029514B2, and CN101466876B published by SUMCO of Japan. SUMCO's patent divides the silicon wafer into several circular areas and determines whether it is a COP defect mode based on the distribution of the number of defects in each circular area. SUMCO's patent does not use the central symmetry of COP and cannot effectively eliminate the influence of silicon wafer processing abnormalities on COP mode determination, so the possibility of misjudgment is high. Summary of the invention

[0008] The present invention mainly solves the deficiencies in the prior art and provides a method for automatically identifying COP and processing defects of single crystal silicon polished wafers. The method realizes batch automatic determination of processing defects and COP defects through program language, thereby solving the problems of difficulty in identifying failure modes and improper product disposal in actual production. The occurrence of COP defects in crystal rods is statistically analyzed, thereby providing an important reference for the adjustment and optimization of crystal pulling conditions.

[0009] The above technical problems of the present invention are mainly solved by the following technical solutions: A method for automatically identifying COP and processing defects of a single crystal silicon polishing wafer comprises the following steps: Step 1: Divide the silicon wafer into 12 sectors with an angle of 30°.

[0010] Step 2: Divide the silicon wafer into three annular areas with radii of zone 1 with a diameter of 0 to 50 mm, zone 2 with a diameter of 50 mm to 100 mm, and zone 3 with a diameter of 100 mm to 150 mm.

[0011] Step 3: Define the coordinate boundaries of each area based on the division methods in steps 1 and 2.

[0012] Step 4: Assign all defects to different areas according to the coordinate file of particle detection.

[0013] Step 5: Count the number of defects in each area.

[0014] Step 6: After removing the maximum and minimum values ​​of the number of defects in each area, calculate the mean and standard deviation of Zone 1, Zone 2, and Zone 3 respectively.

[0015] Step 7: The standard for judging a zone as COP mode is standard deviation / mean < 0.20, otherwise it is a processing defect.

[0016] Preferably, if one of Zone 1 and Zone 3 meets the COP judgment standard, the silicon wafer is in COP mode.

[0017] Preferably, the subdivision mode of COP is further determined, and the subdivision of COP mode is helpful for the optimization and adjustment of the crystal pulling process.

[0018] Preferably, when Zone1 is determined to be in COP mode, it is determined to be a center-aggregated COP mode; when Zone3 is determined to be in COP mode, it is determined to be an outer ring symmetrical distribution COP mode; when Zone1 and Zone3 meet the COP determination criteria and Zone2 does not meet the COP determination criteria, it is a center-aggregated and outer ring symmetrical distribution COP mode; when Zone1, Zone2 and Zone3 all meet the COP determination criteria, they are determined to be a full-surface COP mode; when Zone2 is determined to be in COP mode, it is determined to be a processing defect.

[0019] Preferably, in actual production, one box is regarded as one sub-batch, and a whole box of silicon wafers is stacked and judged; the corresponding crystal rod length is about 25 mm. By statistically analyzing the judgment results of all sub-batches in one crystal rod, the position of the COP crystal segment in the crystal rod is determined, thereby providing an important reference for the adjustment and optimization of crystal pulling conditions.

[0020] Preferably, the coordinates of several consecutive silicon wafers are superimposed together, and then the partition counting and determination are performed according to the above method, thereby increasing the determination accuracy of the COP mode.

[0021] Preferably, when there are a large number of processing defects, stacking the whole box of images will make the defects after stacking tend to be evenly distributed, so that the Stdev standard deviation / Average average value is less than the judgment standard value, thereby causing the result after stacking to be misjudged as COP.

[0022] Preferably, the results of single-image determination and image stacking determination are combined, and when the two determination results are inconsistent, manual intervention is used for determination.

[0023] The present invention can achieve the following effects: The present invention provides an automatic identification method for COP and processing defects of single crystal silicon polished wafers. Compared with the prior art, the present invention realizes batch automatic determination of processing defects and COP defects through program language, thereby solving the problems of difficulty in identifying failure modes and improper product disposal in actual production. The occurrence of COP defects in crystal rods is statistically analyzed, thereby providing an important reference for the adjustment and optimization of crystal pulling conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a map of 16 slightly center-aggregated COP silicon wafers of the present invention.

[0025] Figure 2 This is a map of 16 slightly aggregated COP silicon wafers of the present invention after being stacked.

[0026] Figure 3 This is the determination result of the centrally concentrated COP of the present invention.

[0027] Figure 4 It is the outer ring symmetrical distribution type COP diagram of the present invention.

[0028] Figure 5 This is the outer ring symmetry type COP determination result of the present invention.

[0029] Figure 6 This is a map of 10 consecutive central aggregation + outer ring symmetric partial COPs of the present invention.

[0030] Figure 7 This is a map of 10 consecutive center-aggregated + outer ring symmetrical partial COPs superimposed on each other according to the present invention.

[0031] Figure 8 This is the judgment result after superimposing 10 consecutive center-aggregated + outer ring symmetrically distributed COPs of the present invention.

[0032] Fig. 9 This is a map of the full surface COP of the present invention.

[0033] Fig.10 This is the judgment result of the full surface COP situation of the present invention.

[0034] Fig.11 This is a defect map caused by the polishing abnormality of the present invention.

[0035] Fig.12 This is the determination result of the processing defect caused by the polishing abnormality of the present invention.

[0036] Fig.13 This is a processing defect map caused by polishing abnormality of the present invention.

[0037] Fig.14 This is the determination result of the processing defect caused by the polishing abnormality of the present invention.

[0038] Fig.15 This is a single map of LLS abnormality caused by the final cleaning abnormality of the present invention.

[0039] Fig.16 It is the final cleaning abnormality of the present invention that causes the abnormal LLS whole box stacking.

[0040] Fig.17 This is the determination result of the processing defect caused by the final cleaning abnormality of the present invention.

[0041] Fig.18 This is a map showing data missing in the abnormal area of ​​the present invention.

[0042] Fig.19 This is the determination result when the COP of the present invention and processing defects coexist. DETAILED DESCRIPTION

[0043] The technical solution of the invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0044] Example: Figure 1-19 As shown, a method for automatically identifying COP and processing defects of a single crystal silicon polished wafer includes the following steps: Step 1: Divide the silicon wafer into 12 sectors with an angle of 30°.

[0045] Step 2: Divide the silicon wafer into three annular areas with radii of zone 1 with a diameter of 0 to 50 mm, zone 2 with a diameter of 50 mm to 100 mm, and zone 3 with a diameter of 100 mm to 150 mm.

[0046] Step 3: Define the coordinate boundaries of each area based on the division methods in steps 1 and 2.

[0047] Step 4: Assign all defects to different areas according to the coordinate file of particle detection.

[0048] Step 5: Count the number of defects in each area.

[0049] Step 6: After removing the maximum and minimum values ​​of the number of defects in each area, calculate the mean and standard deviation of Zone 1, Zone 2, and Zone 3 respectively.

[0050] The reason for removing the maximum and minimum values ​​is that when processing abnormalities (such as scratches, residual liquid, etc.) and COP exist at the same time, the abnormal distribution of defects caused by processing abnormalities will lead to a large standard deviation, thereby interfering with the determination of the COP mode. If this silicon wafer only has defects caused by processing and does not have COP, since the defects caused by processing abnormalities are randomly distributed, the standard deviation is still large after removing the maximum and minimum values, so it does not affect the determination result.

[0051] Step 7: The standard for judging whether a zone is in COP mode is standard deviation / mean < 0.20, otherwise it is a processing defect. If one of Zone1 and Zone3 meets the COP judgment standard, the silicon wafer is in COP mode. Further determination of the COP subdivision mode is helpful for the optimization and adjustment of the crystal pulling process.

[0052] When Zone 1 is determined to be in COP mode, it is determined to be a center-concentrated COP mode.

[0053] When Zone 3 is determined to be in COP mode, it is determined to be an outer ring symmetrical distribution type COP.

[0054] When Zone 1 and Zone 3 meet the COP criteria, and Zone 2 does not meet the COP criteria, it is a centrally concentrated and outer ring symmetrically distributed COP mode.

[0055] When Zone 1, Zone 2, and Zone 3 all meet the COP judgment criteria, they are judged as full-face COP mode.

[0056] When Zone2 is determined to be in COP mode, it is determined to be a processing defect.

[0057] In actual production, one box is a sub-batch, and one box contains 25 silicon wafers. A whole box of silicon wafers is stacked and judged; the corresponding crystal rod length is about 25mm. By statistically analyzing the judgment results of all sub-batches in a crystal rod, the position of the COP crystal segment in the crystal rod can be determined, thus providing an important reference for the adjustment and optimization of crystal pulling conditions.

[0058] The coordinates of several consecutive silicon wafers are superimposed together, and then the partition counting and judgment are performed according to the above method, so as to increase the judgment accuracy of the COP mode. When there are a large number of processing defects, stacking the whole box of images will make the defects after stacking tend to be evenly distributed, making the Stdev standard deviation / Average average value less than the judgment standard value, which will cause the result after stacking to be misjudged as COP. Combining the results of single-wafer judgment and stacking judgment, when the judgment results of the two are inconsistent, manual intervention is used for judgment.

[0059] The silicon wafer is divided into several sectors with the same angle, and the silicon wafer is divided into three circular areas with different radii. Whether the defects in a single circular area are evenly distributed in each sector is determined to determine whether the circular area is in COP mode. The size of the "standard deviation / mean" of the number of defects in each sector is used to measure its distribution uniformity. When the "standard deviation / mean" is less than a certain value, it is determined to be COP mode, otherwise it is a silicon wafer processing defect. When calculating the mean and standard deviation of each circular area, the sectors with the largest and smallest number of defects are eliminated, which helps to eliminate the interference of silicon wafer processing abnormalities on the COP mode determination. Since the distribution of processing defects is random, eliminating the maximum and minimum values ​​will not affect the determination results of processing defects.

[0060] In summary, the automatic identification method of COP and processing defects of single crystal silicon polished wafers realizes batch automatic determination of processing defects and COP defects through program language, thereby solving the problems of difficulty in identifying failure modes and improper product disposal in actual production. The occurrence of COP defects in crystal rods is statistically analyzed, thus providing important reference for the adjustment and optimization of crystal pulling conditions.

[0061] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are included in the patent scope of the present invention.

Claims

1. A method for automatically identifying COP and processing defects of a single crystal silicon polished wafer, characterized in that The steps are as follows: Step 1: Divide the silicon wafer into 12 sectors with an angle of 30°; Step 2: Divide the silicon wafer into three annular areas with radii of 0-50mm for zone 1, 50mm-100mm for zone 2, and 100mm-150mm for zone 3; Step 3: Define the coordinate boundaries of each area based on the division method in steps 1 and 2; Step 4: Assign all defects to each area according to the coordinate file of particle detection; Step 5: Count the number of defects in each area; Step 6: After removing the maximum and minimum values ​​of the number of defects in each area, calculate the mean and standard deviation of Zone 1, Zone 2, and Zone 3 respectively; Step 7: The standard for judging a zone as COP mode is standard deviation / mean < 0.20, otherwise it is a processing defect.

2. The method for automatically identifying COP and processing defects of a single crystal silicon polishing wafer according to claim 1, characterized in that: If one of Zone1 and Zone3 meets the COP judgment standard, the silicon wafer is in COP mode.

3. The method for automatically identifying COP and processing defects of a single crystal silicon polishing wafer according to claim 2, characterized in that: The subdivision pattern of COP is further determined, and the subdivision of COP pattern is helpful for the optimization and adjustment of crystal pulling process.

4. The method for automatically identifying COP and processing defects of a single crystal silicon polishing wafer according to claim 3, characterized in that: When Zone1 is determined to be in COP mode, it is determined to be a centrally concentrated COP mode; when Zone3 is determined to be in COP mode, it is determined to be an outer ring symmetrically distributed COP mode; when Zone1 and Zone3 meet the COP determination criteria, and Zone2 does not meet the COP determination criteria, it is a centrally concentrated and outer ring symmetrically distributed COP mode; when Zone1, Zone2, and Zone3 all meet the COP determination criteria, it is determined to be a full-surface COP mode; when Zone2 is determined to be in COP mode, it is determined to be a processing defect.

5. The method for automatically identifying COP and processing defects of a single crystal silicon polishing wafer according to claim 3, characterized in that: In actual production, one box is regarded as a sub-batch, and a whole box of silicon wafers is stacked and judged; the corresponding crystal rod length is about 25mm. By statistically analyzing the judgment results of all sub-batches in a crystal rod, the position of the COP crystal segment in the crystal rod is determined, thus providing an important reference for the adjustment and optimization of crystal pulling conditions.

6. The method for automatically identifying COP and processing defects of a single crystal silicon polishing wafer according to claim 1, characterized in that: The coordinates of several consecutive silicon wafers are superimposed together, and then the partition counting and judgment are performed according to the above method, thereby increasing the judgment accuracy of the COP mode.

7. The method for automatically identifying COP and processing defects of a single crystal silicon polishing wafer according to claim 6, characterized in that: When there are a large number of processing defects, stacking the whole box will make the defects tend to be evenly distributed after stacking, making the Stdev standard deviation / Average average value smaller than the judgment standard value, which will cause the result after stacking to be misjudged as COP.

8. The method for automatically identifying COP and processing defects of a single crystal silicon polishing wafer according to claim 7, characterized in that: The results of single-image judgment and superimposed image judgment are combined. When the two judgment results are inconsistent, manual intervention is used for judgment.

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