Wafer composite scribing process

Abstract

The invention provides a wafer composite scribing process. The wafer composite scribing process comprises the following steps that S1, a modified layer is formed in a wafer cutting channel through focusing of a pulse laser beam; s2, a blade is used for conducting scribing, scribing is conducted on the cutting channel laser marks generated in the step S1, and the newest surface cutting channel is formed under the condition that the modified layer is not cut through; s3, splitting is conducted in sequence along the newest surface cutting channel; a modified layer is formed in a wafer cutting channel through focusing of a pulse laser beam, then a blade is used for cutting into the interior of the cutting channel from the surface of the wafer, and the newest surface cutting channel is formed under the condition that the cutting channel is not cut through. And finally, sequentially carrying out chip splitting along the newest surface cutting channel to obtain a chip with a vertical cutting channel, a complete split chip, a standard size and no edge breakage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wafer dicing, and in particular to a wafer composite dicing process. BACKGROUND

[0002] In the semiconductor process, wafer dicing is a relatively mature technology, and various dicing methods have been derived for wafers of different materials. The conventional wheel dicing method is suitable for most materials on the market, and the cutting effect is relatively ideal, which is the most mature and widely used dicing mode. For some wafers with test metal blocks in the cutting path, the conventional wheel dicing method does not have ideal cutting effect, and the blade will cause large edge collapse when cutting to the metal block, which will damage the effective circuit layer and cause the chip performance to fail.

[0003] In the prior art, there are wheel dicing, laser ablation and laser hidden cutting methods to complete wafer dicing. The wheel dicing method uses a blade to directly physically contact the wafer, and the cutting speed is slow, which is not suitable for processing super-hard materials, and the production efficiency has bottlenecks. Laser ablation uses high temperature generated by laser to melt and re-solidify the materials at the edge of the cutting, which changes the crystal structure and chemical properties of the materials. However, the materials vaporized during processing will melt and re-splatter and deposit on the chip side and surface, forming difficult-to-remove contaminants, and some molten materials may firmly adhere to affect the chip performance and subsequent packaging bonding yield. Laser hidden cutting relies on the light transmittance of the material to make the laser penetrate the material and focus inside. Its application range is limited, and it cannot cut materials with strong light absorption. If there is an angle between the laser scanning direction and the cleavage direction, the crack will not follow the laser scanning path, but will "turn" to find the nearest cleavage plane. This will cause skewed cutting paths, severe edge collapse, incomplete cracking, and inconsistent chip sizes. SUMMARY

[0004] To solve the above problems, the present application provides a wafer composite dicing process.

[0005] The present application is realized by the following technical solutions: The wafer composite dicing process according to the present application comprises the following steps: S1. Forming a modified layer inside the wafer cutting path by focusing a pulsed laser beam; S2. Dicing the cutting path marks generated in step S1 using a blade, and forming a new surface cutting path without cutting through the modified layer; S3. Cracking along the new surface cutting path in sequence.

[0006] Further, in step S1, a modified layer is formed inside the wafer cutting path by focusing a pulsed laser beam: Experiments were conducted using single-point laser and multi-energy frequency stepped laser, and the pulsed laser beam was adjusted to the optimal operating parameters. The pulsed laser beam with the optimal operating parameters was focused inside the wafer, causing the wafer material to be modified and forming a modified layer composed of micro-voids or cracks.

[0007] Furthermore, the pulsed laser beam is focused inside the wafer at a distance of 25 μm from the wafer surface.

[0008] Furthermore, the experiment using single-point laser and multi-energy frequency stepped laser includes: Single-point laser is used, with a feed rate of -50µm, a speed of 600mm / s, and an output power of 0.12W. The first group is focused on a distance of 50µm from the front side of the wafer. A multi-energy frequency stepped laser is used, with feed rates of -10um, -15um, and -25um, speeds of 300mm / s, 600mm / s, and 600mm / s, and output powers of 0.06W, 0.08W, and 0.12W as the second group. These lasers are then focused on different positions within the cutting path, and the laser speed and output power are controlled to be different at each position.

[0009] Furthermore, the angle between the cutting path and the horizontal plane is 45°.

[0010] Furthermore, step S2 also includes: By selecting soft and hard blades at different speeds for dicing, it was confirmed that the chipping size of blades with different hardness was within the standard range, and the most reasonable blade, speed, feed rate, and depth of cut were determined as the optimal operating parameters.

[0011] Furthermore, confirming whether the chipping size of blades with different hardnesses is within the standard range includes: The first experimental group was selected with a soft blade, a rotation speed of 50,000 rpm, a feed rate of 8 mm / s, and a cutting depth of 10 μm. The second experimental group selected a hard blade, a rotation speed of 50,000 rpm, a feed rate of 8 mm / s, and a cutting depth of 10 μm. The third experimental group selected a hard blade, a rotation speed of 35,000-40,000 rpm, a feed rate of 8 mm / s, and a depth of cut of 10 μm. Comparing the three groups of experimental subjects, the group with the smallest front edge chipping size was selected as the optimal operating parameters.

[0012] Furthermore, the laser beam uses 1064nm infrared light.

[0013] Furthermore, the blade width is greater than the width of the pulsed laser bifurcation line.

[0014] The beneficial effects of this invention are: The wafer composite dicing process proposed in this invention first uses a pulsed laser beam to focus and form a modified layer inside the wafer dicing channel. Then, a cutting edge is used to cut from the wafer surface into the dicing channel without cutting through, forming a new surface dicing channel. Finally, dicing is performed sequentially along the new surface dicing channel to obtain chips with vertical dicing channels, complete dicing, standard size, and no chipping. Attached Figure Description

[0015] Figure 1 This is a flowchart of the wafer composite dicing process of the present invention; The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0016] To more clearly and completely illustrate the technical solution of the present invention, the present invention will be further described below with reference to the accompanying drawings.

[0017] Please refer to Figure 1 This invention proposes a wafer composite dicing process comprising the following steps: S1. A modified layer is formed inside the wafer dicing channel by focusing a pulsed laser beam; S2. Use a blade to scribing and scribing the laser marks produced in step S1, forming the newest surface cut marks without cutting through the modified layer; S3. Perform dicing sequentially along the latest surface cutting path.

[0018] In a specific implementation, steps S1-S3 are the initial laser scribing, secondary blade scribing, and chipping, respectively. The energy density at the focal point of the pulsed laser beam is extremely high, causing internal material modification and forming a modified layer composed of micro-voids or cracks. However, due to crystal orientation issues, laser bifurcation occurs during continuous laser focusing, which increases the laser beam width (5-10µm). Direct chipping after laser scribing may cause the bifurcation to extend into the effective metal area, leading to partial chip malfunction. Therefore, the core issue here is to solve the bifurcation problem after laser scribing. Blade scribing is used to solve the bifurcation phenomenon in the dicing channel. After blade scribing, a new dicing groove is formed in the dicing channel, completely covering the laser bifurcation phenomenon. At this time, chipping is performed sequentially along the new dicing groove. The wafer stress has been released during blade scribing, resulting in a regular shape and smooth cut surface during chipping. This prevents bifurcation extension and increased chipping size due to bifurcation, perfectly solving the problem of poor results after laser scribing of wafers with crystal orientation issues, and enabling the acquisition of more complete and standardized chips.

[0019] Furthermore, in step S1, a modified layer is formed inside the wafer dicing channel by focusing a pulsed laser beam: Experiments were conducted using single-point laser and multi-energy frequency stepped laser, and the pulsed laser beam was adjusted to the optimal operating parameters. The pulsed laser beam with the optimal operating parameters was focused inside the wafer, causing the wafer material to be modified and forming a modified layer composed of micro-voids or cracks.

[0020] Furthermore, the experiment using single-point laser and multi-energy frequency stepped laser includes: Single-point laser is used, with a feed rate of -50µm, a speed of 600mm / s, and an output power of 0.12W. The first group is focused on a distance of 50µm from the front side of the wafer. A multi-energy frequency stepped laser is used, with feed rates of -10um, -15um, and -25um, speeds of 300mm / s, 600mm / s, and 600mm / s, and output powers of 0.06W, 0.08W, and 0.12W as the second group. These lasers are then focused on different positions within the cutting path, and the laser speed and output power are controlled to be different at each position.

[0021] In specific implementations, single-shot fixed-point laser dicing offers high efficiency due to its fixed speed and frequency. However, the high hardness and brittleness of SiC-based wafers mean that the modified layer effect after a single-shot laser dicing may be insignificant, directly leading to cleaving after laser scribing. Furthermore, the heat-affected zone of a single-shot laser is difficult to control, resulting in poor dicing performance. In contrast, multi-energy frequency stepped laser dicing, while taking longer, offers greater controllability at each stage. The laser's processing trajectory is not a straight line but rather resembles steps, resulting in a stepped cross-section within the material or after separation. For SiC-based wafers, this scribing method can create a regularly shaped modified layer, significantly reducing the occurrence of rapid edge chipping during cleaving. The energy power of each stage can be adjusted from low to high, and parameters can be adjusted sequentially based on actual laser marks. Through multiple trial adjustments, the optimal dicing effect is achieved, and the final operating parameters are established.

[0022] Furthermore, the pulsed laser beam is focused inside the wafer at a distance of 25 μm from the wafer surface.

[0023] In a specific implementation, the pulsed laser beam is not focused on the surface of the wafer, but inside, so that the wafer material can be modified to form a modified layer. Other distances can also be selected according to actual needs.

[0024] Furthermore, the angle between the cutting path and the horizontal plane is 45°.

[0025] In specific implementations, the angle between the cutting track and the horizontal plane can also be selected from other angles according to actual needs.

[0026] Furthermore, step S2 also includes: By selecting soft and hard blades at different speeds for dicing, it was confirmed that the chipping size of blades with different hardness was within the standard range, and the most reasonable blade, speed, feed rate, and depth of cut were determined as the optimal operating parameters.

[0027] In a specific implementation, since the wafer being processed is a SiC-based wafer with high hardness, the wear is significant when using a soft-blade dicing tool during the dicing process, and there is also a risk of tool breakage during the process. Therefore, soft-blade dicing tools are not suitable for processing wafers of this material.

[0028] Furthermore, confirming whether the chipping size of blades with different hardnesses is within the standard range includes: The first experimental group was selected with a soft blade, a rotation speed of 50,000 rpm, a feed rate of 8 mm / s, and a cutting depth of 10 μm. The second experimental group selected a hard blade, a rotation speed of 50,000 rpm, a feed rate of 8 mm / s, and a cutting depth of 10 μm. The third experimental group selected a hard blade, a rotation speed of 35,000-40,000 rpm, a feed rate of 8 mm / s, and a depth of cut of 10 μm. Comparing the three groups of experimental subjects, the group with the smallest front edge chipping size was selected as the optimal operating parameters.

[0029] In specific implementations, since the wafers being processed are SiC-based wafers with high hardness, the wear is significant when using soft-blade dicing, and there is a risk of blade breakage during the process. Therefore, soft-blade dicing is not suitable for processing wafers of this material. On the other hand, if the speed of hard-blade dicing is too high, the size of wafer edge breakage will be uncontrollable. Therefore, a hard-blade dicing with a low speed is generally used as the cutting edge.

[0030] Furthermore, the laser beam uses 1064nm infrared light.

[0031] Furthermore, the blade width is greater than the width of the pulsed laser bifurcation line.

[0032] In a specific implementation, since the wafer material (SiC) is ultra-brittle and ultra-hard with high mechanical stress, when using a single blade for dicing, the feed rate is required to be very slow (about 3mm / s), and the product quality cannot be fully guaranteed, which greatly reduces the product processing efficiency and product yield. After laser dicing, the laser bifurcation increases the line width (5-10um). At this time, a softer dicing blade (with more diamond particles) with a blade width (17um) greater than the bifurcation line width can be used to dice along the laser marks of the dicing path. It only cuts until the modified layer after laser dicing is not completely cut through. The blade marks can completely cover the laser bifurcation line width and form the new surface dicing path.

[0033] In one embodiment, after the wafer is thinned to the required process thickness, laser grooving can be performed to create new dicing grooves on the dicing surface, breaking down surface stress. Then, a dicing wheel can be used to completely separate the chip. In this process, the blade is less affected by stress during dicing, and the dicing feed speed can be appropriately optimized and increased, thus avoiding the problem of insufficient yield. Alternatively, the wafer can be diced directly using a dicing wheel without thinning, cutting to the required process thickness, and then thinning is performed until the required process thickness is achieved. This method effectively improves chipping on the back side of the chip, but chipping on the front side is uncontrollable. Therefore, this method is used for products with no chipping on the front side but large and uncontrollable chipping on the back side.

[0034] Of course, the present invention may have many other embodiments. Based on this embodiment, other embodiments obtained by those skilled in the art without any creative effort are all within the scope of protection of the present invention.

Claims

1. A wafer composite dicing process, characterized in that, Includes the following steps: S1. A modified layer is formed inside the wafer dicing channel by focusing a pulsed laser beam; S2. Use a blade to scribing and scribing the laser marks produced in step S1, forming the newest surface cut marks without cutting through the modified layer; S3. Perform dicing sequentially along the latest surface cutting path.

2. The wafer composite dicing process according to claim 1, characterized in that, In step S1, a modified layer is formed inside the wafer dicing channel by focusing a pulsed laser beam. Experiments were conducted using single-point laser and multi-energy frequency stepped laser, and the pulsed laser beam was adjusted to the optimal operating parameters. The pulsed laser beam with the optimal operating parameters was focused inside the wafer, causing the wafer material to be modified and forming a modified layer composed of micro-voids or cracks.

3. The wafer composite dicing process according to claim 2, characterized in that, The pulsed laser beam is focused inside the wafer at a distance of 25 μm from the wafer surface.

4. The wafer composite dicing process according to claim 1, characterized in that, The experiments using single-point laser and multi-energy frequency stepped laser include: Single-point laser is used, with a feed rate of -50µm, a speed of 600mm / s, and an output power of 0.12W. The first group is focused on a distance of 50µm from the front side of the wafer. A multi-energy frequency stepped laser is used, with feed rates of -10um, -15um, and -25um, speeds of 300mm / s, 600mm / s, and 600mm / s, and output powers of 0.06W, 0.08W, and 0.12W as the second group. These lasers are then focused on different positions within the cutting path, and the laser speed and output power are controlled to be different at each position.

5. The wafer composite dicing process according to claim 4, characterized in that, The S2 step further includes: By selecting soft and hard blades at different speeds for dicing, it was confirmed that the chipping size of blades with different hardness was within the standard range, and the most reasonable blade, speed, feed rate, and depth of cut were determined as the optimal operating parameters.

6. The wafer composite dicing process according to claim 1, characterized in that, The process of confirming whether the chipping size of blades with different hardnesses is within the standard range includes: The first experimental group was selected with a soft blade, a rotation speed of 50,000 rpm, a feed rate of 8 mm / s, and a cutting depth of 10 μm. The second experimental group selected a hard blade, a rotation speed of 50,000 rpm, a feed rate of 8 mm / s, and a cutting depth of 10 μm. The third experimental group selected a hard blade, a rotation speed of 35,000-40,000 rpm, a feed rate of 8 mm / s, and a depth of cut of 10 μm. Comparing the three groups of experimental subjects, the group with the smallest front edge chipping size was selected as the optimal operating parameters.

7. The wafer composite dicing process according to claim 2, characterized in that, The laser beam uses 1064nm infrared light.

8. The wafer composite dicing process according to claim 1, characterized in that, The angle between the cutting track and the horizontal plane is 45°.

9. The wafer composite dicing process according to claim 1, characterized in that, The blade width is greater than the width of the pulsed laser bifurcation line.

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