Crystal wafer system and method

Abstract

A method for producing wafers or discs from industrially produced crystals, said method comprising the following steps: scanning the volume of the crystal (1), forming a 3D volumetric digital model of the crystal; -recording 3D spatial coordinates of the defects (4, 4 ') detected during the scanning process; -measuring one or more crystal axes (C1, C2, C3) provided by the crystal structure of the crystal and recording said crystal axes in a 3D model of said crystal; -withdrawing one or more crystal cores (2) from the crystal (1) in a selected crystal direction parallel to or at an angle to one of the crystal axes; -slicing the crystal core orthogonally to the selected crystal direction with a wafer slicer, the wafer slicer comprising a slicing tool comprising a plurality of cutting wires or blades spaced apart by a regular slicing pitch (G) for cutting wafers of the same thickness (S) from the crystal core; -wherein the method comprises calculating an offset position (O) of the slicing tool along the selected crystal axis, the offset position being configured to have a minimum number of defective wafers, and-adjusting the position of the slicing tool relative to the crystal core in the selected crystal direction as a function of the calculated offset.

Description

Field of the Invention

[0001] The present invention relates to a method for wafering crystals, in particular large crystals such as sapphire, silicon or silicon carbide crystals for optical or electronic applications. Background of the Invention

[0003] Industrially produced crystals, such as sapphire crystals, usually weigh from a few kilograms to several hundred kilograms and have an irregular shape that is approximately conical / cylindrical. In this irregular 3D shape, Figure 1 The photo shows an industrially produced sapphire crystal. A typical process is to extract cylindrical cores, which are then cut into discs or round wafers (such as Figure 2 ). The axis of the cylindrical core is oriented in a defined direction relative to the crystal structure of the crystal, for example, it may correspond to an optical axis of the crystal. Typically, industrial applications require a disk or wafer of a certain diameter and thickness, and the position and number of the cylindrical cores may vary from one raw crystal to another, depending on the size and shape of the raw crystal.

[0004] It should be understood that, in general, the extracted core may have a circular, rectangular or any other cross-section. It should also be understood that "disc" or "wafer" is a general term for parallel slices of the core, regardless of its shape or thickness.

[0005] In traditional processes, the crystal structure axes are determined through measurements using X-rays or optical measurement tools, and the optimal distribution of cores is extracted from a specific crystal, leaving it up to a human operator to decide on the best layout.

[0006] However, these processes are time-consuming and costly. In addition, due to defects within the crystal, a certain amount of waste is generated, which ends up in the disks or wafers cut from the selected core. Since the production of such crystals is time-consuming and expensive, it is advantageous to reduce the amount of waste and defective disks or wafers. SUMMARY OF THE INVENTION

[0008] In view of the above, an object of the present invention is to provide a system and method for crystal wafering for industrial production to reduce waste and improve the yield of the wafering process.

[0009] It would be advantageous to provide a wafer processing process for industrially produced crystals that can produce very high quality crystal disks or wafers with low defect rates.

[0010] Advantageously, a fast and economical process for wafering crystals for industrial production is provided, particularly with improved automation and reduced manual intervention.

[0011] The object of the present invention is achieved by the crystal wafering method according to claim 1 .

[0012] A method for producing wafers from industrially produced crystals is disclosed, the method comprising the following steps:

[0013] -Scan the volume of the crystal to form a 3D volume digital model of the crystal;

[0014] Record the 3D spatial coordinates of defects detected during scanning;

[0015] - measuring one or more crystal axes (C1, C2, C3) provided by the crystal structure of the crystal and recording said crystal axes in the 3D model of said crystal;

[0016] - removing one or more cores from the crystal in a selected crystal axis direction, said direction being parallel to one of said crystal axes or forming a certain angle with said crystal axis;

[0017] - slicing the wafer core orthogonally to the selected crystal direction using a wafer slicer, the wafer slicer comprising a slicing tool, the slicing tool comprising a plurality of cutting lines or blades spaced at a regular slicing pitch (G) for slicing wafers of uniform thickness (S) from the wafer core;

[0018] Wherein, the method comprises

[0019] - calculating an offset position (O) of the slicing tool along a selected crystal direction, said offset position being configured to have a minimum number of defective disks or wafers, and

[0020] - Adjust the position of the slicing tool relative to the core along the selected crystal direction according to the calculated offset.

[0021] In one embodiment, the magnitude of the offset position varies from 0 to the slice gap (G) thickness of the wafer.

[0022] In an advantageous embodiment, the scanning of the crystal comprises an optical scanning of the crystal.

[0023] In an advantageous embodiment, the core is placed on a support, and the support and the core are placed in a microtome.

[0024] In an advantageous embodiment, after the crystal core is cut out of the crystal, the crystal core axis is measured again, and the position of the crystal core axis is adjusted by the support so that the slicing tool cuts the wafer orthogonally to the adjusted crystal axis.

[0025] In an advantageous embodiment, cores of maximum diameter (Dmax) are cut from the crystal such that the minimum number of defects is found in the wafers to be cut from the crystal by calculation using the 3D volumetric digital model.

[0026] In an advantageous embodiment, the absolute value of the offset is calculated based on a reference position on the crystal surface before the coring operation.

[0027] In an advantageous embodiment, the step of scanning the crystal for defects and geometry is performed after coring the top and / or bottom end of the original crystal.

[0028] In a preferred embodiment, the crystal includes multiple crystal axes, and the method includes generating a plane intersecting the crystal core or wafer, the plane is parallel to the axis of the crystal core and orthogonal to the crystal axis, calculating the number of defects between the plane and the outer contour of the crystal core or wafer, and selecting one of the planes for slicing, and the number of defects in the removal area between the plane and the outer contour is the largest.

[0029] In a preferred embodiment, a non-circular pattern, such as a semiconductor chip pattern cut from a wafer, is oriented according to one of a plurality of calculated crystal axes (C2, C3) such that a minimum number of defects are found within the area of ​​the chip or within a minimum number of chips and a maximum number of defects are found within a removed area between the outer contour of the chip pattern and the outer circular periphery of the wafer.

[0030] In an advantageous embodiment, the chip pattern is included in a 3D volume digital model of the crystal for calculating an offset to take into account defects in the scrap area between the outer diameter of the wafer and the chips to be cut from the wafer.

[0031] Also disclosed herein is a system for producing wafers from industrially produced crystals, the system comprising:

[0032] a scanner for scanning the volume of the crystal, and a program module for forming a 3D volume digital model of the crystal based on the output of the scanner;

[0033] The program module is further configured to record the 3D spatial coordinates of defects detected by the scanner;

[0034] Wherein the program module is configured to calculate an offset position (O) of a slicing tool along a selected crystal axis, the selected crystal axis being configured to have a minimum number of defective wafers.

[0035] In an advantageous embodiment, the scanner used to scan the crystal comprises an optical scanner.

[0036] In an advantageous embodiment, the system further comprises:

[0037] A measuring device for measuring one or more crystal axes (C1, C2, C3) provided by the crystal structure of a crystal and recording the one or more crystal axes in a 3D model of the crystal.

[0038] In an advantageous embodiment, the system further comprises:

[0039] A crystal core extraction device, the crystal core extraction device is used to cut out one or more cylindrical crystal cores (2) from the crystal (1) in the direction of a selected crystal axis; and

[0040] A wafer slicer comprises a slicing tool comprising a plurality of cutting lines or blades spaced apart at a regular slicing pitch (G) for slicing wafers of uniform thickness (S) from a wafer core.

[0041] The system may be configured to perform the method for producing a wafer as described in any of the above embodiments.

[0042] Other objects and advantages of the present invention will be apparent from the claims, the following detailed description and the accompanying drawings.

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Photo of an industrially produced sapphire crystal.

[0045] Figure 2 Schematic diagram of the wafering process of a known industrially produced crystal, describing the original crystal and the crystal cores at selected positions, and the process of cutting one of the crystal cores into a circular disk.

[0046] Figure 2a A simplified schematic diagram of the core cutting tool and crystal.

[0047] Figure 2b A simplified perspective diagram of a cylindrical wafer placed on a wafer holder being cut into discs by a wire slicer.

[0048] Figure 3a Schematic diagram of a cylindrical core cut from a raw crystal before being cut into disks, with some defects within the core.

[0049] Figure 3b A simplified schematic diagram of the cutting grid and wafer in the core of a crystal.

[0050] Figure 3c For similar Figure 3a , showing the Figure 3a Schematic diagram of the optimal cutting arrangement for the defect shown in .

[0051] Figure 3d for Figure 3a Schematic diagram of a non-optimized cutting arrangement of an embodiment.

[0052] Figure 4 This is a planar schematic diagram of the crystal core, which requires a plane parallel to the cylinder axis.

[0053] Figure 5 Schematic plan view of a wafered semiconductor disk, such as a silicon carbide crystal, showing the locations of the semiconductor chips to be cut from the disk.

[0054] Figure 6 FIG. 2 is a block diagram illustrating a method according to an embodiment of the present invention.

[0055] Detailed description of the invention

[0056] Referring to the accompanying drawings, the industrially produced raw crystal 1 has a roughly conical irregular 3D shape 9 and has a crystal structure that defines one or more crystal axes corresponding to a specific orientation of the lattice. For example, in sapphire crystal, there is an optical axis (also commonly referred to as the c-axis) C1, which eliminates the inherent birefringence characteristics of sapphire crystal. The selected crystal axis C1 can also be located in the crystal plane that is most resistant to forces applied perpendicular to the plane. This plane is 20% more difficult to process than other crystallographic orientations. In many applications, it is necessary to cut the wafer at a specific angle to one or more axes (for example, orthogonal to the optical axis C1).

[0057] For semiconductor circuits, the orientation of the crystal lattice is also important, and the wafer should be cut along a specific direction in the crystal. The lattice orientation can be determined by various well-known measurement means, such as using optical or x-ray measurement systems.

[0058] Once the axis is determined, the cylindrical core can be oriented within the original crystal volume and discs or wafers cut from it. In many applications, the required wafer diameter Dn is predetermined, and from the original crystal, wafers of different diameters or surface areas can be extracted for potentially different applications or the same application. Using sapphire crystals as an example, wafers of different diameters can be used to produce lenses of different sizes for optical instruments. Typically, wafers with larger diameters are more valuable and rarer, so the number of wafers extracted from each original crystal is obviously smaller (sometimes only one).

[0059] After the selected core is determined, the cylindrical cores 2, 2a, 2b, 2c may be cut using an appropriate core cutting tool 6.

[0060] For the subsequent wafer slicing process, the die is typically placed in a polymer holder or support 8 which is bonded to the crystalline die and disappears during the wafer slicing process.

[0061] The support 8 may be manufactured by an additive process such as 3D printing or by a molding process or a subtractive process, for example machined from a block of support material and adjusted to the shape and size of the core. In this regard, although the crystal axis (such as the optical axis C1) is determined to extract the core, its measurement may be slightly inaccurate and can be further corrected by the position of the core 2 in the support 8. This will allow, for example, the wafer to be cut orthogonally to the measured crystal axis C1 with greater accuracy, the support 8 being located in a wafer slicer.

[0062] A disk or wafer slicer is typically formed of multiple wires (usually diamond-coated wires or blades) arranged at regular intervals and slicing the wafer core orthogonally to a particular direction (eg, the optical axis).

[0063] It is worth noting that the crystal core direction can be defined as a crystal axis, but it is not always equal to a crystal axis. For example, in some applications, sapphire is cut at an angle of 20.5 degrees to the optical axis. The term "crystal direction" used herein corresponds to the "crystal core direction", which, as mentioned above, can be parallel to the lattice axis or at a certain angle relative to the lattice axis.

[0064] Cooling and lubricating fluids may be used during the coring and slicing process, which typically takes several hours or days. The coring and slicing process of the wafer itself is a well-known process and does not need to be described further in this article. The two discs at the end of the core can be removed as scrap and the slices are then typically re-inspected to determine if there are no defects or those with defects below an acceptable threshold, with those with defects above the threshold being rejected. In many industrial wafer processing processes, it is typical that about 5% to 30% of the sliced ​​discs are rejected due to internal crystal defects, but this depends largely on the quality of the crystal itself and the diameter of the disc or wafer.

[0065] According to one aspect of the invention, prior to the coring process, but optionally after the gem cutting and top and bottom grinding or slicing processes, the crystal is fully 3D scanned and the three-dimensional X, Y, Z coordinates of each defect within the crystal volume are mapped. These X, Y, Z coordinates can be mapped relative to a fixed geometric reference (point, line, surface) to the crystal or to the edge of the core. The original crystal or a support fixed to the original crystal can be marked with reference points or shapes. Thus, a digital 3D model of the crystal can be constructed and the defects can be located therein.

[0066] The crystal axes are measured by known measuring instruments (eg using x-rays), and these crystal axis directions are also recorded in a digitized 3D model of the crystal.

[0067] Cores can then be selected to cut the crystal in the direction of the chosen crystal axis, and the positions of the cores can be optimized to ensure that the most valuable cores (i.e., the largest cores) have the fewest defects within their volume. This optimization can be performed with the help of a computer program that seeks to minimize the number of defects in a core of a given diameter by varying the position of the cores in the original crystal and counting the number of defects at each position.

[0068] Thus, the computer-aided optimization process can be configured to place the largest diameter core in the optimal position, i.e., the position with the least amount of defects within the core volume, and then place the remaining smaller diameter cores in the remaining volume around the largest core. If there is a largest core and a second largest core, and then there are cores of smaller size than the second largest core, then the optimization process can position the second largest core in the optimal position with the least amount of defects within that core before positioning the remaining cores. Depending on the application, the cores can have a predetermined diameter, or their diameters can vary from a single large core with the largest possible diameter and other smaller diameter cores in the original crystal to optimize the volume of useful material and reduce the volume of waste material. The latter will depend on the requirements of the wafer for the intended application. Alternatively, the optimization can be performed to collectively maximize the value of all extracted cores.

[0069] Figure 3a A core is shown, for example a core of maximum diameter Dmax extracted from an original crystal, having a useful volume 10 from which wafers can be cut orthogonally to the crystal axis C1. As mentioned above, wafers are usually required for specific applications and need to have a certain thickness S, and such wafers can be cut using a wire saw with a regular cutting grid.

[0070] According to one aspect of the invention, depending on the position of the cutting grid along the crystal axis, there may be a certain number of discs with defects 4, ranging between a minimum number of discs with defects and a maximum number of discs with defects. The spacing between the cutting lines corresponds to the range of possible axial positions of the cutting lines and can be adjusted to optimize the number of defect-free discs (i.e., discs with no defects or only defects below an acceptable threshold defined by the application requirements).

[0071] According to one aspect of the invention, the position of the cutting lines is adjusted by an offset O, which is in the range between 0 and the grid spacing G between the cutting lines 7. The offset O is an absolute value added from a reference plane or reference point, such as the end face 5 of the core or any other fixed reference point or shape on the original crystal 1, the crystal core 2 or the support 8. The process can be automated in a simple manner using a digital 3D model of the crystal, in which the X, Y, Z position of the defect and the crystal axis orientation are recorded, so that the optimal offset can be calculated at any time before wafer slicing, including before taking the crystal core 2 from the original crystal 1. The position of the offset O can be adjusted according to any other reference position, such as a reference position provided on the core support. The offset position and position correction of the crystal relative to the machine can be achieved by repositioning the core on the support, or adjusting the geometry of the support to present a reference surface thereon, which adjusts the position of the support 8 relative to the sawing machine, or sending instructions to the sawing machine to adjust the position of the support so that the calculated offset accurately positions the reference position of the cutting grid relative to the core or its support.

[0072] When calculating the offset, the thickness of material removed during the slicing process is taken into account, whereby the optimization process may vary the offset from 0 to the grid spacing G to determine the number of wafer slices having defects below a predetermined acceptable threshold, whereby some defects may be within the material removed by the thickness B and therefore no longer exist in the wafer, or defects that may have existed in two adjacent wafers are transferred to a single wafer.

[0073] exist Figure 3c In Figure 3a Taking the defect found in the embodiment of as an example, the offset is calculated from a reference point on an outer point of the crystal surface 9, and the corresponding offset is 68.5mm. As a result, defects are found in 3 of the 18 wafer slices. These 3 wafers are Figure 3c In this particular example, if a non-optimal offset of 69.5 mm is used, 6 wafer slices contain defects ( Figure 3d ). Therefore, an important advantage is that this embodiment can calculate the optimal offset and offset the position of the linear grid along the selected crystal axis to reduce waste. In addition, by scanning the defect and then 3D modeling the spatial coordinates of the defect, and the crystal axis and the crystal outer contour as reference points, the optimal cutting arrangement can be automatically and accurately adjusted to reduce waste.

[0074] Reference Figure 4In some applications, a plane is required that is parallel to the cylinder axis and orthogonal to a crystal axis or crystal direction. In some crystals, such an axis or direction is replicated by crystal symmetry, and therefore a plurality of equivalent directions C1.1, C1.2, C1.3 are provided to locate the plane. In such applications, the spatial coordinates of the defects 4, 4' can also be used to optimize the selection of the flat cutting planes 13a, 13b, 13c that form the cylinder chord, to produce a flat chord surface in the waste volume 11 with the most defects 4'. The flat chord surface cut from a core or wafer disc can be used for various applications, including, for example, marking the lattice orientation in a semiconductor crystal.

[0075] refer to Figure 5 The spatial coordinates of the defects 4, 4' can also be used to optimize the choice of the cutting offset and the subsequent orientation of the chip according to one of the equivalent crystal directions C2.1, C2.2 (e.g. parallel or orthogonal to the crystal axis) from which the chip can be geometrically oriented by rotating the surface area covered by the chip 12 so that as many inclusions as possible are found in the waste area 11 between the outer periphery of the chip and the rectangular contour. Figure 4 In the illustrated embodiment, the chip 12 is preferably oriented according to the crystal direction C2.2 rather than the crystal axis C2.1, because in the first angular orientation aligned with the crystal direction C22, the area covered by the chip 12 has fewer defects 4 than in the second angular orientation C2.1, and in the second angular orientation, the area covered by the chip 12' has more defects 4'.

[0076] If the crystal is used as Figure 5 For the illustrated application of chip extraction, such as extracting semiconductor chips from a silicon carbide crystal, the offset can also be adjusted to take into account inclusions at the periphery and inclusions found in the waste volume 11 between the circular periphery of the disk wafer and the actual chip.

[0077] Serial number list:

[0078] Core Extraction Machine

[0079] Crystal Core Cutting Tool6

[0080] Slicer

[0081] Cutting line 7

[0082] Crystal support 8

[0083] 3D inspection machine

[0084] Original Crystal 1

[0085] Outer contour / surface 9

[0086] Useful volume 10

[0087] Waste volume 11

[0088] Defect 4

[0089] Flat cut 13

[0090] Cylindrical crystal core 2, 2a, 2b, 2c

[0091] End face 5

[0092] Reference surface disk / wafer 3

[0093] Chip 12

[0094] Crystal axes C1, C2, C3

[0095] For example, the optical axis

[0096] Equivalent crystal directions C1.1, C1.2, C1.3 and C2.1, C2.2 such as crystal axis and core diameter Dn

[0097] Disc or wafer slice thickness S

[0098] Cutting blade thickness B

[0099] OffsetO

Claims

1. A method for producing wafers or disks from industrially produced crystals, the method comprising the following steps: - scanning the volume of the crystal (1) to form a 3D volume digital model of the crystal; - Record the 3D spatial coordinates of the defects (4,4') detected during the scanning process; - measuring one or more crystal axes (C1, C2, C3) provided by the crystal structure of the crystal and recording said crystal axes in the 3D model of said crystal; - removing one or more crystal cores (2) from the crystal (1) in a selected crystal direction, said direction being parallel to one of said crystal axes or forming a certain angle with said crystal axis; - slicing the wafer core orthogonally to the selected crystal direction using a wafer slicer, the wafer slicer comprising a slicing tool, the slicing tool comprising a plurality of cutting lines or blades spaced at a regular slicing pitch (G) for slicing wafers of uniform thickness (S) from the wafer core; - wherein the method comprises calculating an offset position (O) of the slicing tool along a selected crystal direction, the offset position being configured to have a minimum number of defective wafers, and - Adjust the position of the slicing tool relative to the core along the selected crystal direction according to the calculated offset.

2. The method according to the preceding claim, characterized in that The magnitude of the offset position varies from 0 to the slice pitch (G) thickness of the wafer.

3. A method according to any preceding claim, characterised in that Scanning of the crystal includes optical scanning of the crystal.

4. A method according to any preceding claim, characterised in that The wafer core (2) is placed on a support (8), and the support and wafer core are placed in a slicer.

5. The method according to the preceding claim, characterized in that After the core is cut out of the crystal, the core axis is measured again, and the position of the core axis is adjusted by the bracket so that the slicing tool cuts the wafer orthogonally to the adjusted crystal axis.

6. A method according to any preceding claim, characterised in that The cores of maximum diameter (Dmax) cut from the crystal allow the minimum number of defects to be found in the wafers to be cut from the crystal by calculation using the 3D volumetric digital model.

7. A method according to any preceding claim, characterised in that The absolute value of the offset is calculated from a reference position on the crystal surface before the coring operation.

8. A method according to any preceding claim, characterised in that The step of scanning the crystal for defects and geometry is performed after coring the top and / or bottom of the original crystal.

9. A method according to any preceding claim, characterised in that The crystal includes multiple equivalent crystal axes or multiple equivalent crystal directions (C1.1, C1.2, C1.3). The method includes generating a plane (13a, 13b, 13c) intersecting with a crystal core or a wafer, wherein the plane is parallel to the axis of the crystal core and orthogonal to the crystal axis, calculating the number of defects between the plane and the outer contour of the crystal core or the wafer, selecting one of the planes for slicing, and the number of defects (4') in the waste area (11) between the plane and the outer contour is the largest.

10. A method according to any preceding claim, characterised in that A non-circular pattern, such as a pattern for semiconductor chips (12) cut from a wafer (3), is oriented according to one of a plurality of calculated crystal directions (C2.1, C2.2) so that the number of defects (4) found in the area of ​​the chip or in a minimum number of chips is minimal and the number of defects found in the waste area (11) between the outer contour of the chip pattern and the outer circumference of the wafer is maximal.

11. The method according to the preceding claim, characterized in that The chip pattern is included in a 3D volume digital model of the crystal and is used to calculate an offset to take into account defects in the scrap area (11) between the outer diameter of the wafer and the chips to be cut from the wafer.

12. A system for producing wafers from industrially produced crystals, the system comprising: a scanner for scanning the volume of a crystal (1), and a program module for forming a 3D volume digital model of the crystal based on the output of the scanner; The program module is further configured to record the 3D spatial coordinates of the defects (4, 4') detected by the scanner; Wherein the program module is configured to calculate an offset position (O) of a slicing tool along a selected crystal axis, the selected crystal axis being configured to have a minimum number of defective wafers.

13. System according to the preceding claim, characterised in that The system further comprises: A measuring device for measuring one or more crystal axes (C1, C2, C3) provided by the crystal structure of a crystal and recording the one or more crystal axes in a 3D model of the crystal.

14. System according to any one of the two preceding claims, characterized in that The system further comprises: A crystal core extraction device, the crystal core extraction device is used to cut out one or more cylindrical crystal cores (2) from the crystal (1) in the direction of a selected crystal axis; and A wafer slicer comprises a slicing tool comprising a plurality of cutting lines or blades spaced apart at a regular slicing pitch (G) for slicing wafers of uniform thickness (S) from a wafer core.

15. A system according to any one of the three preceding claims, characterised in that The system is configured to perform the method according to any one of claims 1-11.

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