CN114643411A

CN114643411A - Multi-focus laser forming method for through hole

Info

Publication number: CN114643411A
Application number: CN202011494823.6A
Authority: CN
Inventors: 洪详竣
Original assignee: E&R ENGINEERING CORP
Current assignee: E&R ENGINEERING CORP
Priority date: 2020-12-17
Filing date: 2020-12-17
Publication date: 2022-06-21

Abstract

The invention provides a method for forming multi-focus laser of a through hole, which comprises the following steps: forming a pre-through hole on a substrate by multifocal laser, wherein the pre-through hole is formed by laser processing according to a plurality of focuses generated by the multifocal laser, the multifocal laser forms an ablation area and a modification area at each focus by laser, each ablation area is communicated with and forms the pre-through hole, each modification area surrounds each ablation area, the multifocal laser emits a plurality of laser beams by a laser source, and then the plurality of laser beams are reflected by a vibrating mirror (scanning head), so that the plurality of laser beams form the plurality of focuses on the substrate; immersing the substrate containing the pre-through hole in an etching tank for etching to adjust the diameter psi of the pre-through hole₁A through hole of (2).

Description

Multi-focus laser forming method for through hole

Technical Field

A method for forming a through hole, and more particularly to a method for forming a multi-focus laser of a through hole.

Background

The electronic industry is continuously evolving, and various electronic devices are gradually becoming thinner, smaller and smaller in shape while pursuing high quality, in terms of semiconductor chips, the semiconductor chips are usually made of semiconductor materials such as silicon or gallium arsenide, and in the past, the semiconductor chips were two-dimensional integrated circuits (2D ICs) and used Wire Bonding technology (Wire Bonding) and Flip Chip package (Flip Chip), however, the circuit patterns of the semiconductor chips are gradually reduced to tens of nanometers along with the technological evolution, and the number of wires and the number of signal pins are increased, so that the difficulty of Wire Bonding is increased, moreover, the flip chip packaging technique can only package a single chip, which is difficult to deal with the number of signal pins required by the semiconductor chip, therefore, three-dimensional integrated circuits (3D ICs) are developed to break through the structural limitations of two-dimensional ICs and achieve higher performance than two-dimensional ICs.

Currently, a three-dimensional integrated circuit is mainly a Silicon interposer made of Through Silicon Vias (TSVs), and conductive materials are filled in the Through Silicon vias to connect a plurality of vertically stacked chips, so as to achieve the number of wirings required by a high-performance semiconductor chip and the density of input/output pins, thereby showing the importance of the technology for forming the Through vias.

In order to form a fine through hole having a long and flat hole diameter on a substrate in the process technology for forming the through hole, a person skilled in the art uses a Bessel Beam (Bessel Beam) laser technology to ablate the substrate, and forms a micro hole having a high aspect ratio on the substrate with a light intensity distribution characteristic of a Bessel Beam long focal depth.

However, compared with the general laser technology, the bessel beam is a long beam formed by a laser source through elements such as a cone Lens (Axicon Lens), a plurality of lenses and a Spatial Filter (Spatial Filter), because the installation position of each element and the distance between each element need to be calculated in advance, if any element used for generating the bessel beam is changed, the positions of the other elements need to be adjusted accordingly, so that the focal point of the bessel beam is difficult to change by changing the angle of a single element or the assistance of an auxiliary element after being positioned, when a plurality of through holes are required to be formed on the substrate, the position of the substrate needs to be continuously moved, the focal point of the bessel beam can fall on a region of the substrate where the through holes are to be formed, and the laser path is not changed by an instrument generating the laser to form the through holes in sequence, but the machine is difficult to accurately adjust the distance in millimeter level, the time consumed by moving the substrate by the machine is more than the time consumed by adjusting the laser path by an instrument, which further prolongs the laser processing time and affects the operation efficiency of forming the through hole, so that there is a need for further improvement of the current laser method for forming the slender through hole.

Disclosure of Invention

In view of this, the present invention provides a method for forming a multi-focus laser of a through hole, which uses a multi-focus laser technology to replace the conventional bessel beam to form the through hole, so as to avoid the situation that the forming operation efficiency is affected by the time for moving the substrate due to the fact that the path of the bessel beam cannot be adjusted.

To achieve the above object, the method for forming a multi-focus laser of a through hole of the present invention comprises:

forming a pre-through hole on a substrate by multifocal laser, wherein the pre-through hole is formed by laser processing according to a plurality of focuses generated by the multifocal laser, the multifocal laser forms an ablation area and a modification area at each focus by laser, each ablation area is communicated to form the pre-through hole, each modification area surrounds each ablation area, the multifocal laser emits a plurality of laser beams from a laser source, and the plurality of laser beams are reflected by a vibrating mirror (scanning head) to form the plurality of focuses on the substrate;

immersing the substrate containing the pre-through hole in an etching tank for etching to adjust the diameter psi of the pre-through hole₁A through hole of (2).

The multifocal laser technology of the present invention can form the plurality of focuses on the substrate and perform laser processing instead of the conventional bessel beam to form the micro-holes with high aspect ratio on the substrate, and can change the positions of the plurality of focuses by adjusting the emitting angle of the multifocal laser by the vibrating mirror compared with the bessel beam which is difficult to change the laser path when a plurality of through holes are required to be formed on the substrate, thereby improving the working efficiency when a plurality of through holes are formed.

Drawings

FIG. 1: the invention discloses a multi-focus laser forming method of a through hole.

FIG. 2 is a schematic diagram: schematic side view of laser machining with multi-focal laser.

FIG. 3A: the side view of the substrate forming the pre-through hole is schematically shown.

FIG. 3B: the invention is a side view schematic diagram of a focus formed by converging laser on a substrate.

FIG. 3C: a schematic side view of an ablation zone in the present invention.

FIG. 3D: in another embodiment, the side view of the ablation region and the modification region is schematically shown.

FIG. 4: the substrate of the present invention is a schematic top plan view of a pre-through hole.

FIG. 5: the invention is a schematic plan view of a through hole formed by etching.

FIG. 6: the pre-through hole is etched to generate a schematic top plan view of impurities.

Detailed Description

Referring to fig. 1, the method for forming a multi-focus laser of a through hole of the present invention includes:

step S101: referring to fig. 2 to 4, a pre-through hole 12 is formed on a substrate 10 prepared in advance by using multi-focus laser, wherein the pre-through hole 12 is formed by laser processing according to a plurality of focuses 11 generated by the multi-focus laser. Referring to fig. 2, the multi-focus laser technology used in the present invention is that a laser source 20 emits a plurality of laser beams 21, and the plurality of laser beams 21 are reflected by a vibrating mirror (scanning head)30, the vibrating mirror 30 may be a multi-focus laser vibrating mirror, such that the plurality of laser beams 21 form a plurality of focuses 11 linearly arranged from the surface to the inside of the substrate 10, and the plurality of focuses 11 may be simultaneously formed on the substrate 10 and laser processing is simultaneously performed at each focus 11 to form the pre-through hole 12, and the vibrating mirror 30 may adjust the reflection path of the plurality of laser beams 21 by two internal mirrors 31, thereby moving the positions where the plurality of focuses 11 are formed on the substrate 10, wherein the plurality of focuses 11 are arranged along an axial direction of the substrate.

Referring to fig. 3A, 3B and 3C together, in step S101, when the substrate 10 is ablated by the multi-focus laser at the plurality of focal points 11, as shown in fig. 3B, fig. 3B only uses one focal point 11 as an example, since each focal point 11 is the focus of two lasers 21, and the multi-focus laser forms an ablation area 13 in the hourglass shape shown in fig. 3C at each focal point 11, as shown in fig. 3A, the plurality of focal points 11 are arranged in a straight line and consecutively, so that each ablation area 13 is communicated with each other from the top surface of the substrate 10 to the bottom surface of the substrate 10 to form the pre-through hole 12, it should be noted that fig. 3A, 3B and 3C are enlarged schematic diagrams of each focal point 11 and each ablation area 13, and the micro-holes formed by the multi-focus laser in the present invention are communicated with each ablation area 13, in another embodiment, when the focal points 11 are closely arranged with a shortened interval therebetween, the ablation regions 13 of the hourglass shape may overlap and communicate with each other to form the pre-through holes 12.

The diameter psi in FIG. 3A, FIG. 3B, FIG. 3C and FIG. 4 is preset on the substrate 10₁The shape, size and position of the circumference 14 correspond to the shape, size and position of a through hole to be formed, the plurality of focal points 11 are formed within the circumference 14, and the number of the plurality of focal points 11 depends on the thickness of the substrate 10 or the required depth of the through hole. In the embodiment, the plurality of focal points 11 are formed at the central position of the circumference 14, so the central position of the pre-through hole 12 formed by the plurality of focal points 11 is equal to the central position of the circumference 14, but the forming positions of the plurality of focal points 11 are not limited thereto. In the present embodiment, the plurality of focal points 11 may be arranged on the same straight line, and the straight line corresponds to the desired shape and position of the through hole, so as to form the slender and straight pre-through hole 12 by laser ablation, but the arrangement of the plurality of focal points 11 is not limited thereto.

On the other hand, while the laser processing heats the substrate 10 by using heat energy to vaporize or melt a portion of the substrate 10 to form each ablation region 13, the heat energy of the pressure wave of the laser also affects the surrounding portion of the substrate 10 around each ablation region 13, so that the substrate 10 is deformed in the surrounding area of each ablation region 13 to form a modified region 15, or heat affected zone, and each modified region 15 is located between the circumference 14 and the pre-through hole 12 to surround each ablation region. In one embodiment, the width of each ablation region 13 may be 0.3 μm, and the width of each modification region 15 may be 2 μm to 5 μm.

Referring to fig. 3D, in another embodiment, taking laser processing is performed by forming a first focal point 11A and a second focal point 11B on the substrate 10 with multifocal laser, the multifocal laser forms a first ablation region 13A and a first modified region 15A at the first focal point 11A, the multifocal laser forms a second ablation region 13B and a second modified region 15B at the second focal point 11B, and according to the difference between the first focal point 11A and the second focal point 11B, the first ablation region 13A and the first ablation region 13B can overlap and communicate with each other to form the pre-through hole 12, and the first modified region 15A and the second modified region 15B also overlap each other.

Step S102: the substrate 10 including the pre-through hole 12 is immersed in a first etching bath for a first-stage etching, wherein the etching rate of the first etching bath is V1, and the first etching bath may contain an etching solution of a strong acid solution such as hydrofluoric acid (HF), hydrochloric acid, sulfuric acid, or nitric acid.

Step S103: as shown in fig. 5, the substrate 10 after the first-stage etching is immersed in a second etching tank for the second-stage etching, and the pre-through hole 12 on the substrate 10 is adjusted to have a diameter ψ by the first-stage etching and the second-stage etching₁The shape, size and position of the through hole 18 correspond to the circumference 14 shown in fig. 3A and 4, and the etching rate of the second etching tank is V2, and the second etching tank can contain an etching solution of a strong acid solution such as hydrofluoric acid (HF), hydrochloric acid, sulfuric acid or nitric acid, wherein the etching rate V1 of the first etching tank is less than the etching rate V2 of the second etching tank, i.e., the first etching tank can be a low-speed etching tank, the second etching tank is a high-speed etching tank relative to the first etching tank, and the etching rate V1 of the first etching tank and the etching rate V2 of the second etching tank can be controlled by the concentration and ratio of the components such as hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid, etc. in the etching solution.

Referring to fig. 6, in steps S102 and S103, when the substrate 10 is immersed in the etching solution, the etching solution can etch and remove the rough portion on the surface of each pre-through hole 12, on the other hand, since the structure in the modified region 15 has been changed by the heat energy of the laser, the structure of the portion of the substrate 10 in the modified region 15 is relatively fragile, the etching solution can etch and remove the portion of the substrate 10 in the modified region 15, so as to avoid the generation of cracks in the portion of the modified region 15, while the first etching pool or the second etching pool can decompose the portion of the substrate 10 in the modified region 15 by the etching solution, the decomposed portion is changed into the impurity 16, and when the substrate 10 is immersed in the first etching pool or the second etching pool for etching, the first etching pool or the second etching pool can be further ultrasonically oscillated to remove the impurity 16 generated by etching from the surfaces of the substrate 10 and the pre-through hole 12, the impurities 16 are prevented from being accumulated to influence the etching operation.

The etching rate V1 of the first etching pool is set to be smaller than the etching rate V2 of the second etching pool, so that the aperture of the pre-through hole 12 formed in step S101 is smaller, if the etching rate of the pre-through hole 12 during the first-stage etching is too fast, the amount of the impurities 16 generated by the action of the etching liquid in unit time is too large, which easily affects the chip removal efficiency of the pre-through hole 12, the impurities are easily accumulated in the pre-through hole 12 to block the pre-through hole 12, and the etching liquid cannot flow into the pre-through hole 12 again to increase the aperture of the pre-through hole 12 by the etching action, thereby affecting the etching quality and efficiency; on the other hand, the two ends of the pre-through hole 12 and the surface of the substrate 10 have a connection 17 shown in fig. 3A, and since each connection 17 is a boundary between the surface of the substrate 10 and the inner surface of the pre-through hole 12, the etching liquid etches each connection 17 from the surface of the substrate 10 and the inner surface of the pre-through hole 12 at the same time, when the etching time is long, the etching rate of each connection 17 is easily made to be greater than the etching rate of the inner surface of the pre-through hole 12, and the first-step etching causes the aperture at the two ends of the pre-through hole 12 to be greater than the aperture at the middle section of the pre-through hole 12, and the two ends of the pre-through hole 12 will form a trumpet shape, size and position respectively, so that the pre-through hole 12 cannot form the shape, size and position of the through hole 18 to be formed after the second-step etching.

Therefore, in the present invention, the substrate 10 including the pre-through hole 12 is subjected to the first-stage etching at a low etching rate in step S103 to remove a portion of the modified region 15 on the substrate 10, and then the substrate 10 including the pre-through hole 12 is subjected to the second-stage etching to etch the remaining modified region 15 at a high 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 by the high etching rate, thereby avoiding the problem that the substrate 10 including the pre-through hole 12 is too thin due to too long etching.

Calculating a first etching time required for the first-stage etching of the pre-through hole 12 and a second etching time required for the second-stage etching by using the etching rate V1 of the first etching pool and the etching rate V2 of the second etching pool, wherein the first etching time and the second etching time can be respectively preset values, and the time ratio or distribution of the first etching time and the second etching time can be adjusted according to the shape, size and position of the through hole 18 to be formed and the thickness and material of the substrate 10, when the substrate 10 is etched in the first etching pool for the first etching time, the substrate 10 is taken out from the first etching pool and immersed in the second etching pool, and when the substrate 10 is etched in the second etching pool for the second etching time after the first-stage etching, the substrate 10 is etched to form the through hole 18 in the second stage, that is, the substrate 10 is taken out from the second etching bath, so as to prevent the through hole 18 from being unable to conform to the required shape, size or position due to over-etching.

In summary, the present invention replaces the bessel beam used in the prior art with the multi-focus laser, and forms the thin and long micro-holes with high aspect ratio by forming the plurality of focuses 11 on the substrate 10 for ablation, and the multi-focus laser used in the present invention can adjust the positions of the plurality of focuses 11 by the galvanometer 30, and when a plurality of through holes are required to be formed on the substrate 10, the time required for the galvanometer 30 to finely adjust the two mirrors 31 inside is much faster than the time required to adjust the positions of the substrate 10, so that the working efficiency when forming the plurality of through holes can be improved.

Claims

1. A method for forming a multi-focus laser of a through hole, comprising:

forming a pre-through hole on a substrate by multifocal laser, wherein the pre-through hole is formed by laser processing according to a plurality of focuses generated by the multifocal laser, the multifocal laser forms an ablation area and a modification area at each focus by laser, each ablation area is communicated with the pre-through hole, each modification area surrounds each ablation area, the multifocal laser emits a plurality of laser beams by a laser source, and then the plurality of laser beams are reflected by a vibrating mirror, so that the plurality of laser beams form the plurality of focuses on the substrate;

immersing the substrate containing the pre-through hole in an etching tank for etching to adjust the diameter psi of the pre-through hole₁A through hole.

2. The method of claim 1, wherein the step of etching the substrate with the pre-through hole by immersing the substrate in an etching bath comprises:

immersing the substrate containing the pre-through hole in a first etching pool to carry out first-stage etching;

immersing the substrate after the first-stage etching in a second etching tank for second-stage etching to adjust the diameter psi of the pre-through hole₁The through-hole of (2).

3. The method of claim 1, wherein the plurality of focal points are arranged on a same line.

4. The method of claim 1, wherein the multi-focal laser is formed by adjusting a reflection path of the multi-channel laser by the galvanometer to move the plurality of focal points on the substrate.

5. The method of claim 2, wherein the etching rate of the first etching bath is less than the etching rate of the second etching bath.

6. The method of claim 2, wherein the step of etching the substrate with the pre-through hole by immersing the substrate with the pre-through hole in a first etching bath completes a first etching step after the substrate with the pre-through hole is etched for a first etching time.

7. The method of claim 2, wherein the step of etching the substrate by immersing the substrate in a second etching bath for a second etching time after the first etching step, the pre-through hole is adjusted to have a diameter ψ₁The through-hole of (2).

8. The method of claim 1 wherein each of said ablated regions overlaps each other and each of said modified regions overlaps each other.