TWI744135B - Multi-focus laser forming method of through hole - Google Patents

Abstract

The multi-focus laser forming method of the through hole of the present invention includes: a multi-focus laser forms a pre-through hole on a substrate, wherein the pre-through hole is formed by laser processing according to the multiple focus points generated by the multi-focus laser , The multi-focus laser laser forms an ablation zone and a modification zone at each focal point, each ablation zone is connected to form the pre-through hole, and each modification zone surrounds each ablation zone, wherein, The multi-focus laser emits a complex laser from a laser source, and then reflects the complex laser through a scanning head, so that the complex laser is shot on the substrate to form the complex focal point; the substrate is immersed in an etching tank is etched, so that the pre-adjusted to the diameter of the through hole of the through hole ₁ a ψ.

Description

Multi-focus laser forming method of through hole

A method for forming a through hole, especially a method for forming a through hole by a multi-focus laser.

The electronics industry is constantly evolving. While all kinds of electronic components are pursuing high quality, they are gradually becoming lighter, thinner and shorter. In the case of semiconductor chips, semiconductor chips are usually composed of semiconductor materials such as silicon or gallium arsenide. In the past, semiconductor chips It is a two-dimensional integrated circuit (2D IC) that uses wire bonding and flip chip packaging. However, the circuit pattern of the semiconductor chip gradually shrinks to tens of nanometers as the technology evolves, and the number of wires and signal connections The increase in the number of pins makes wire bonding more difficult, and flip-chip packaging technology can only encapsulate single-layer chips, which is difficult to cope with the number of signal pins required by semiconductor chips. Therefore, three-dimensional integrated circuits (3D ICs) have been developed to break through the two-dimensional The structure limitation of the integrated circuit achieves higher performance than the two-dimensional integrated circuit.

At present, three-dimensional integrated circuits are mainly made of silicon through-holes (Through Silicon Via, TSV) made of silicon interposers. Conductive materials are filled in the silicon through-holes to connect vertically stacked multiple chips to realize high-efficiency semiconductor chips. The number of wiring required and the density of input and output pins show the importance of forming through-hole technology.

Regarding the process technology of forming through holes, in order to form tiny through holes with slender and flat apertures on the substrate, many companies use Bessel Beam laser technology to ablate the substrate. The light intensity distribution characteristics of the depth of focus form micropores with a high aspect ratio on the substrate.

However, compared with general laser technology, Bessel beam is a long beam formed by laser light source passing through conical lens (Axicon Lens), complex lens and spatial filter (Spatial Filter). The distance between the setting position and each component needs to be calculated in advance. If any component used to generate the Bessel beam is changed, the positions of the other components need to be adjusted accordingly, making the Bessel beam difficult to penetrate after the focus is positioned. Change the angle of a single component or change the position with the assistance of auxiliary components. Therefore, when multiple through holes need to be formed on the substrate, the position of the substrate must be constantly moved so that the focus of the Bessel beam can fall on the next substrate to form a through hole. Instead of changing the laser path by the instrument that generates the laser to form the through hole in the area of the hole, it is difficult for the machine to accurately adjust the distance in millimeters. It is more expensive to move the substrate by the machine than to adjust the laser path by the instrument. More time, which in turn causes the laser processing time to be prolonged, and affects the efficiency of forming through holes. Therefore, it is necessary to further improve the current laser method for forming slender through holes.

In view of this, the present invention proposes a through-hole multi-focus laser forming method. The multi-focus laser technology replaces the conventional Bessel beam to form the through hole to avoid the inability to adjust the path of the Bessel beam and cause movement. It happens that the time of the substrate affects the efficiency of the forming operation.

In order to achieve the foregoing objective, the multi-focus laser forming method of the through hole of the present invention includes: a multi-focus laser forms a pre-through hole on a substrate, wherein the pre-through hole is based on the complex focus generated by the multi-focus laser Formed by laser processing, the multi-focus laser laser forms an ablation zone and a modified zone at each of the focal points, each of the ablation zones is connected to form the pre-through hole, and each of the modified zones surrounds each of the burned areas. Eroded area, where the multi-focus laser emits a complex laser from a laser source, and then reflects the complex laser through a scanning head, so that the complex laser forms the complex focus on the substrate; the substrate is immersed in the pre-etch tank through hole is etched, so that the pre-adjusted to the diameter of the through hole of the through hole ₁ a ψ.

The multi-focus laser technology of the present invention can form the multiple focal points on the substrate and perform laser processing instead of the conventional Bessel beam to form high-diameter-depth-ratio micro-holes on the substrate. In the case of a complex through hole, compared with the Bessel beam, which is difficult to change the laser path, the multi-focus laser technology can adjust the emission angle of the multi-focus laser through the galvanometer to change the position of the complex focus. , In order to improve the work efficiency when forming a plurality of through holes.

Please refer to FIG. 1, the multi-focus laser forming method of the through hole of the present invention includes:

Step S101: Referring to FIGS. 2 to 4, a pre-through hole 12 is formed on a pre-prepared substrate 10 with a multi-focus laser, wherein the pre-through hole 12 is a complex number generated by the multi-focus laser The focal point 11 is formed by laser processing. As shown in FIG. 2, the multi-focus laser technology used in the present invention emits multiple lasers 21 from a laser source 20, and then reflects the lasers 21 through a scanning head 30. 30 can be a multi-focus laser galvanometer, so that the lasers 21 form the plurality of focal points 11 in a linear arrangement from the surface to the inside of the substrate 10, and the plurality of focal points 11 can be formed on the substrate 10 at the same time. Laser processing is performed at each focal point 11 to form the pre-through hole 12, and the galvanometer 30 can adjust the reflection path of the lasers 21 through the two mirrors 31 inside, thereby moving the multiple focal points 11 to be formed on the substrate 10, where the multiple focal points 11 are arranged along an axial direction of the substrate.

With reference to FIGS. 3A, 3B, and 3C, in step S101, when a multi-focus laser is used to ablate the substrate 10 at the plurality of focal points 11, as shown in FIG. 3B, only one of the focal points is used in FIG. 11 as an example, since each focal point 11 is the focus of two lasers 21, the multi-focus laser will form an hourglass-shaped ablation zone 13 at each focal point 11 as shown in Fig. 3C, so as shown in Fig. 3A As shown, the plurality of focal points 11 are continuously arranged along a straight line, so that each of the ablation regions 13 from the top surface of the substrate 10 to the bottom surface of the substrate 10 communicate with each other to form the pre-through hole 12. It should be noted that FIG. The enlarged schematic view of the focal point 11 and each of the ablation zones 13, in a macro view, the pre-through hole 12 formed by a multi-focus laser in the present invention is an elongated micro-hole formed by the communication of the ablation zones 13, and In another embodiment, when the distance between the focal points 11 is shortened and arranged closely, the ablation regions 13 of the hourglass shape can overlap and communicate with each other to form the pre-through hole 12.

_{The substrate 10 is preset with a circle 14 of diameter ψ 1} in Figs. 3A, 3B, 3C and 4, and the shape, size and position of the circle 14 correspond to the shape, size and position of a through hole to be formed , And the plurality of focus points 11 are formed within the range of the circumference 14, the number of the plurality of focus points 11 depends on the thickness of the substrate 10 or the required depth of the through hole and other conditions. In this embodiment, the complex focus 11 is formed at the center of the circumference 14, so the center position of the pre-through hole 12 formed through the complex focus 11 is equal to the center position of the circumference 14, but the formation of the complex focus 11 The location is not limited to this. In this embodiment, the plurality of focal points 11 can be arranged on the same straight line, and the straight line corresponds to the required shape and position of the through hole to form the elongated and straight pre-through hole 12 through laser ablation, but the The arrangement of the multiple focal points 11 is not limited to this.

On the other hand, laser processing uses thermal energy to heat the substrate 10 to vaporize or melt part of the substrate 10 to form each ablation zone 13. At the same time, the pressure wave thermal energy of the laser also affects the substrate 10 on each of the substrates. The surrounding area of the ablation zone 13 causes the substrate 10 to undergo qualitative transformation in the surrounding area of each ablation zone 13 to form a modified zone 15, or heat-affected zone. The through holes 12 surround each ablation zone. In one embodiment, the width of each of the ablation regions 13 may be 0.3 μm, and the width of each of the modified regions 15 may be 2 μm to 5 μm.

Further referring to FIG. 3D, in another embodiment, a first focus 11A and a second focus 11B are formed on the substrate 10 by a multi-focus laser for laser processing as an example, and the multi-focus laser is placed on the first focus 11A and a second focus 11B. A first ablation zone 13A and a first modification zone 15A are formed at a focal point 11A, a second ablation zone 13B and a second modification zone 15B are formed at the second focal point 11B by a multi-focus laser, and According to the distance between the first focal point 11A and the second focal point 11B, the first ablation zone 13A and the first ablation zone 13B can overlap and communicate with each other to form the pre-through hole 12, and the first modified zone 15A And the second modified region 15B also overlap each other.

Step S102: Immerse the substrate 10 containing the pre-through hole 12 in a first etching bath for first-stage etching. The etching rate of the first etching bath is V1, and the first etching bath may contain hydrofluoric acid ( HF), hydrochloric acid, sulfuric acid or nitric acid and other strong acid etching solutions.

Step S103: As shown in FIG. 5, the substrate 10 after the first-stage etching is immersed in a second etching bath for second-stage etching, and the pre-through hole 12 on the substrate 10 passes through the first-stage etching and the second etching. The second-stage etching is adjusted to _{the through hole 18 with a diameter of ψ 1.} The shape, size and position of the through hole 18 correspond to the circumference 14 shown in FIGS. 3A and 4, and the etching process is completed, and the second etching pool The etching rate of is V2, and the second etching bath may contain an etching solution of strong acid such as hydrofluoric acid (HF), hydrochloric acid, sulfuric acid or nitric acid, wherein the etching rate V1 of the first etching bath is less than that of the second etching bath The etching rate V2 means that the first etching pool can be a low-speed etching pool, and the second etching pool is a high-speed etching pool relative to the first etching pool, and the etching rate of the first etching pool is V1 And the etching rate V2 of the second etching bath can be controlled by conditions such as the concentration and ratio of hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid and other components in the etching solution.

Please refer to FIG. 6, in steps S102 and S103, when the substrate 10 is immersed in an etching solution, the etching solution can etch and remove the roughness of the surface of each pre-through hole 12. On the other hand, due to the modified region 15 The internal structure has been changed by the thermal energy of the laser, making the structure of the substrate 10 in the modified region 15 weaker. The etching solution can etch away the substrate 10 in the modified region 15 to avoid modification. Cracks are generated in the area 15 and the first etching bath or the second etching bath will decompose the substrate 10 in the modified area 15 by the etching solution, and the decomposed part will be turned into impurities 16, and when the substrate 10 When immersed in the first etching bath or the second etching bath for etching, the first etching bath or the second etching bath can be further oscillated with ultrasonic waves to facilitate the removal of impurities 16 produced by etching away from the substrate 10 and the surface of the pre-through hole 12 to prevent impurities 16 from accumulating and affecting the etching operation.

The purpose of setting the etching rate V1 of the first etching pool to be lower than the etching rate V2 of the second etching pool is that the aperture of the pre-through hole 12 formed in step S101 is small, and if the pre-through hole 12 is subjected to the first-stage etching When the etching rate is too fast, there are too many impurities 16 generated by the etching solution in a unit time, which easily affects the chip removal efficiency of the pre-through hole 12, and the impurities are easy to accumulate in the pre-through hole 12, causing the pre-through hole 12 to block , The etching solution can no longer flow into the pre-through hole 12 by etching to increase the aperture size of the pre-through hole 12, which affects the etching quality and efficiency; on the other hand, both ends of the pre-through hole 12 and the surface of the substrate 10 There is a connection 17 shown in FIG. 3A. Since each connection 17 is the junction between the surface of the substrate 10 and the inner surface of the pre-through hole 12, the etching solution flows from the surface of the substrate 10 and the pre-through hole 12 at the same time. The inner surface of each connection 17 is etched. When the etching time is long, the etching rate of each connection 17 is likely to be greater than the etching rate of the inner surface of the pre-through hole 12, and the first-stage etching causes the pre-through hole The aperture at both ends of the pre-through hole 12 is larger than the aperture in the middle section of the pre-through hole 12, and the two ends of the pre-through hole 12 will form a horn shape respectively, so that the pre-through hole 12 cannot be formed after the second-stage etching. The shape, size and location of the hole 18.

Therefore, the present invention uses step S103 to perform a first-stage etching on the substrate 10 containing the pre-through hole 12 at a lower etching rate, to remove part of the modified region 15 on the substrate 10, and then to perform the first-stage etching on the substrate 10 containing the pre-through hole. The substrate 10 of 12 is subjected to a second-stage etching, the remaining modified region 15 is etched at a higher etching rate, and the pre-through hole 12 is etched and adjusted to conform to the shape, size and position of the through hole 18 to be formed , And the etching operation for forming the through hole 18 is completed in a short time with a higher etching rate, so as to avoid the problem that the substrate 10 containing the pre-through hole 12 is too thin after being etched for too long.

According to the etching rate V1 of the first etching pool and the etching rate V2 of the second etching pool, a first etching time required for the first-stage etching of the pre-through hole 12 and a second-stage etching required for the pre-through hole 12 can be calculated The first etching time and the second etching time can be respectively a preset value, and the time ratio or distribution of the first etching time and the second etching time can be based on the through-hole to be formed The shape, size and position of the hole 18 and the thickness and material of the substrate 10 are adjusted. When the substrate 10 has been etched in the first etching bath for the first etching time, it represents that the substrate 10 has completed the first-stage etching. That is, the substrate 10 is taken out from the first etching bath and immersed in the second etching bath, and when the substrate 10 after the first-stage etching has been etched in the second etching bath for the second etching time, it represents The second-stage etching of the substrate 10 is completed to form the through hole 18, that is, the substrate 10 is taken out of the second etching bath to prevent the through hole 18 from being over-etched and failing to meet the required shape, size, or position.

In summary, the present invention replaces the Bessel beam used in the conventional technology with a multi-focus laser, and ablation is performed by forming the multiple focus 11 on the substrate 10 to form elongated micro-holes with a high-diameter ratio, and The multi-focus laser used in the present invention can adjust the position of the multiple focal points 11 by the galvanometer 30. In the case where a plurality of through holes need to be formed on the substrate 10, the galvanometer 30 can fine-tune the two mirrors 31 inside. The time required is much faster than the time to adjust the position of the substrate 10, which can improve the work efficiency when forming a plurality of through holes.

10: substrate

11, 11A, 11B: focus

12: Pre-through hole

13, 13A, 13B: ablation zone

14: circumference

15, 15A, 15B: modified area

16: Impurities

17: Connection

18: Through hole

20: Laser source

21: Laser

30: Galvanometer

31: Mirror

Fig. 1: Step flow chart of the multi-focus laser forming method of the through hole of the present invention. Figure 2: A schematic side view of a multi-focus laser performing laser processing. Fig. 3A: A schematic side view of the pre-through hole formed in the substrate of the present invention. Fig. 3B: A schematic side view of the laser converging on the substrate to form a focal point in the present invention. Figure 3C: A schematic side view of the ablation zone in the present invention. Fig. 3D: A schematic side view of the ablation zone and the modified zone in another embodiment. Fig. 4: A schematic top plan view of the pre-through hole formed on the substrate in the present invention. Fig. 5: A schematic top plan view of a through hole formed by etching in the present invention. Fig. 6: A schematic top plan view of the impurity generated by the etching of the pre-through hole in the present invention.

Claims (7)

A multi-focus laser forming method of a through hole includes: a multi-focus laser forms a pre-through hole on a substrate, wherein the pre-through hole is formed by laser processing according to the multiple focus points generated by the multi-focus laser , The multi-focus laser laser forms an ablation zone and a modification zone at each focal point, each ablation zone is connected to form the pre-through hole, and each modification zone surrounds each ablation zone, wherein, The multi-focus laser emits a complex laser from a laser source, and then reflects the complex laser through a scanning head, so that the complex laser is shot on the substrate to form the complex focal point; The substrate is immersed in an etching bath for etching, so that the pre-through hole is adjusted to _{a through hole with a diameter of ψ 1} ; wherein, the multi-focus laser is adjusted by the galvanometer to adjust the reflection path of the complex laser to move the complex focus to form The position on the substrate. According to the multi-focus laser forming method of a through hole according to claim 1, the step of immersing the substrate containing the pre-through hole in an etching bath for etching includes: immersing the substrate containing the pre-through hole in a first tank for a first etching step etching; and through the substrate after the first etch step is immersed in a second pool of a second etching step etching, so that the pre-adjusted to the diameter of the through hole of the through-ψ ₁ hole. According to the multi-focus laser forming method of the through hole described in claim 1, the plurality of focus points are arranged on the same straight line. According to the multi-focus laser forming method of the through hole according to claim 2, the etching rate of the first etching pool is lower than the etching rate of the second etching pool. According to the multi-focus laser forming method of the through hole according to claim 2, the substrate containing the pre-through hole is immersed in a first etching bath for etching, and the substrate containing the pre-through hole is etched After reaching a first etching time, the first-stage etching is completed. According to the multi-focus laser forming method of the through hole according to claim 2, the substrate after the first-stage etching is immersed in a second etching bath for etching, and the substrate is etched to a second etching time, the pre-adjusted through hole diameter of the through hole of ψ _1. According to the multi-focus laser forming method of the through hole as described in claim 1, the ablation regions overlap each other, and the modified regions overlap each other.

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