Characterization method for internal structure of through hole in chip

Abstract

The invention discloses a characterization method for the internal structure of a through hole in a chip, and relates to the technical field of chip advanced packaging, and the characterization method comprises the following steps: providing an interposer wafer, setting a cutting path on the interposer wafer, and enabling the cutting path to pass through at least one through hole; a laser beam is focused on the cutting path of the interposer wafer, so that the wafer material on the cutting path is heated and sublimated under irradiation of the laser beam, a modified area is obtained, and modified points and cracks are formed in the modified area; the interposer wafer is broken along the cutting path, and a cut interposer wafer is obtained; and observing the internal structure of the through hole in the cut interposer wafer. The characterization method is simple in step, the chip can be rapidly cut to expose the inner wall of the through hole, and the cutting effect is good.

Description

Technical Field

[0001] The present invention relates to the technical field of advanced chip packaging, and in particular to a method for characterizing the internal structure of a through hole in a chip. Background Art

[0002] 2.5D / 3D packaging and chiplets are currently the most advanced packaging technologies. They usually require a silicon substrate (TSV) or a glass substrate (TGV) as an intermediary layer to achieve in-plane or vertical interconnection between chips. They are an effective means to achieve the shortest and most dense interconnection path between chips.

[0003] The preparation steps of TGV / TSV include: pre-fabricate circuits and devices on the wafer surface, perform through-hole etching, deposit an insulating layer on the inner wall of the etched through-hole, then fill the insulating layer with conductive metal, and finally polish. Among them, the thickness, uniformity and step coverage of the insulating layer on the sidewall of the TSV / TGV through-hole are related to the performance of the device, and the surface roughness of the sidewall of the through-hole after etching is closely related to the quality of the subsequent metal coating.

[0004] However, the current method for detecting the internal structure of the through hole has a poor cracking effect. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for characterizing the internal structure of a through hole in a chip, aiming to solve the problem of poor chipping effect in the method for detecting the internal structure of a through hole in the prior art.

[0006] To achieve the above object, the present invention proposes a method for characterizing the internal structure of a through hole in a chip, wherein the chip includes an interposer wafer, and the interposer wafer is provided with a through hole penetrating the interposer. The method for characterizing the internal structure of the through hole in the chip includes the following steps:

[0007] S10, providing an interposer wafer, and setting a cutting path on the interposer wafer, wherein the cutting path passes through at least one of the through holes;

[0008] S20, focusing the laser beam onto the cutting path of the interposer wafer, so that the temperature of the wafer material on the cutting path increases and sublimates under the irradiation of the light beam, thereby obtaining a modified region, wherein the modified region is formed with modified points and cracks;

[0009] S30, breaking the interposer wafer along the cutting path to obtain a cut interposer wafer;

[0010] S40, observing the internal structure of the through hole in the cut interposer wafer.

[0011] In one embodiment, step S20 includes: focusing the laser beam to one end of a cutting path of the interposer wafer, and moving the laser beam to the other end along the cutting path.

[0012] In one embodiment, the power of the laser beam is less than 1 W.

[0013] In one embodiment, the moving speed of the laser beam is A, 0<A<1000mm / s.

[0014] In one embodiment, the diameter of the modified dots is less than 5 μm.

[0015] In one embodiment, the material of the interposer wafer includes a glass substrate, and step S30 includes:

[0016] Mechanical stress is applied to the cutting route to increase the cracks in the modified region until the glass substrate breaks.

[0017] In one embodiment, the method of applying mechanical stress includes lifting the film expander.

[0018] In one embodiment, the method of applying mechanical stress includes lifting a film spreader, and the height of the lifting of the film spreader is 20-50 μm.

[0019] In one embodiment, step S40 includes: observing the internal structure of the through hole in the cut interposer wafer by means of a scanning electron microscope.

[0020] In the technical solution of the present invention, in step S10, a cutting path is first set on the interposer wafer, and a suitable cutting path can be found under a microscope. The cutting path must pass through one or more through holes. The cutting path can be along the diameter direction of the through hole, preferably cut along the diameter of the through hole, so that a larger and easier to observe inner wall of the through hole can be obtained. In step S20, the laser beam is focused on the cutting path of the interposer wafer. At this time, the laser beam can be irradiated along the depth direction of the through hole, or along the diameter direction of the through hole. At the same time, the laser beam can be at least one continuously moving laser beam, or it can be irradiated by multiple fixed laser beams. When the laser beam contacts the wafer material on the cutting path, a multi-photon absorption effect will occur, and then it will heat up and sublimate. The heated and sublimated part will form a modified point and crack, so that the cutting path becomes a modified area, which is easy to break. In step S30, the method of breaking the interposer wafer along the cutting route can be to apply mechanical force or thermal stress to release the internal stress of the interposer wafer material, thereby breaking it. In step S40, an internal structure image of the through hole can be obtained by observation, and structural information of the through hole can be obtained from the internal structure image. By the laser cutting method of the present invention, the silicon substrate or glass substrate is precisely split at the through hole opening, the cutting speed is fast, the cutting effect is good, and the internal morphology of the TSV / TGV exposed after cutting is relatively complete, which is suitable for the characterization of the TSV / TGV through hole morphology. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0022] Figure 1 This is a diagram of the internal structure observed under a scanning electron microscope after the through hole of the silicon substrate in Example 1 provided by the present invention is laser cut;

[0023] Figure 2 This is a diagram of the internal structure observed under a scanning electron microscope after the through hole of the silicon substrate in Example 2 provided by the present invention is laser cut;

[0024] Figure 3 This is a diagram of the internal structure observed under a scanning electron microscope after the through hole of the silicon substrate in Example 3 provided by the present invention is cut;

[0025] Figure 4 This is a diagram of the internal structure observed under a scanning electron microscope after the through hole of the glass substrate in Example 4 provided by the present invention is cut;

[0026] Figure 5This is a diagram of the internal structure observed under a scanning electron microscope after FIB cutting of the through hole of the silicon substrate in Comparative Example 1 provided by the present invention;

[0027] Figure 6 This is a diagram of the internal structure observed under a metallographic microscope after the through hole of the silicon substrate in Comparative Example 2 provided by the present invention is polished by a grinder and polisher;

[0028] Figure 7 This is a diagram of the internal structure of the through hole of the glass substrate observed under a metallographic microscope after being ground by a grinder and polisher in Comparative Example 3 provided by the present invention.

[0029] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0030] To make the purpose, technical scheme and advantages of the embodiment of the present invention clearer, the technical scheme in the embodiment of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiment, it is carried out according to the normal conditions or the conditions recommended by the manufacturer. If the reagents or instruments used do not specify the manufacturer, they are all conventional products that can be purchased commercially. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes, taking "A and / or B" as an example, including scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, the technical schemes between the various embodiments can be combined with each other, but must be based on the ability of ordinary technicians in the field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that the combination of such technical solutions does not exist, and is not within the scope of protection required by the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present invention.

[0031] 2.5D / 3D packaging and chiplets are currently the most advanced packaging technologies. They usually require a silicon substrate (TSV) or a glass substrate (TGV) as an intermediary layer to achieve in-plane or vertical interconnection between chips. They are an effective means to achieve the shortest and most dense interconnection path between chips.

[0032] The preparation steps of TGV / TSV include: pre-fabricate circuits and devices on the wafer surface, perform through-hole etching, deposit an insulating layer on the inner wall of the etched through-hole, then fill the insulating layer with conductive metal, and finally polish. Among them, the thickness, uniformity and step coverage of the insulating layer on the sidewall of the TSV / TGV through-hole are related to the performance of the device, and the surface roughness of the sidewall of the through-hole after etching is closely related to the quality of the subsequent metal coating.

[0033] However, the current methods for detecting the internal structure of through-holes have poor chipping effects. Specifically, there are two existing chipping methods: (1) Focused ion beam system (FIB), which has the disadvantage of slow cutting speed, resulting in high sample characterization costs, and easily causing damage to the filling material inside the through-hole or poor filling. (2) Grinding and polishing machine chipping. This method has a very fast cutting speed, but the surface of the sample processed by the grinding and polishing machine is rough and unclean. This roughness will interfere with microscopic observation, making it difficult to discern details and may also affect the accuracy of the measurement. In addition, the speed of the grinding and polishing machine processing is uncontrollable, which can easily damage the original structure inside the through-hole.

[0034] In view of this, the present invention provides a method for characterizing the internal structure of a through hole in a chip, wherein the chip includes an interposer wafer, wherein the interposer wafer is provided with a through hole penetrating the interposer, and the method for characterizing the internal structure of the through hole in the chip includes the following steps:

[0035] S10, providing an interposer wafer, and setting a cutting path on the interposer wafer, wherein the cutting path passes through at least one of the through holes;

[0036] S20, focusing the laser beam onto the cutting path of the interposer wafer, so that the temperature of the wafer material on the cutting path increases and sublimates under the irradiation of the light beam, thereby obtaining a modified region, wherein the modified region is formed with modified points and cracks;

[0037] S30, breaking the interposer wafer along the cutting path to obtain a cut interposer wafer;

[0038] S40, observing the internal structure of the through hole in the cut interposer wafer.

[0039] In the technical solution of the present invention, in step S10, a cutting path is first set on the interposer wafer, and a suitable cutting path can be found under a microscope. The cutting path must pass through one or more through holes. The cutting path can be along the diameter direction of the through hole, preferably cut along the diameter of the through hole, so that a larger and easier to observe inner wall of the through hole can be obtained. In step S20, the laser beam is focused on the cutting path of the interposer wafer. At this time, the laser beam can be irradiated along the depth direction of the through hole, or along the diameter direction of the through hole. At the same time, the laser beam can be at least one continuously moving laser beam, or multiple fixed laser beams can be irradiated together. The wafer material on the cutting path contacted by the laser beam will undergo a multi-photon absorption effect, and then it will heat up and sublimate. The heated and sublimated part will form a modified point and crack, so that the cutting path becomes a modified area, which is easy to break. In step S30, the method of breaking the interposer wafer along the cutting path can be to apply mechanical force or thermal stress to release the internal stress of the interposer wafer material, thereby breaking it. In step S40, an internal structure image of the through hole can be obtained by observation, and structural information of the through hole can be obtained from the internal structure image. By the laser cutting method of the present invention, the silicon substrate or glass substrate is precisely split at the through hole opening, the cutting speed is fast, the cutting effect is good, and the internal morphology of the TSV / TGV exposed after cutting is relatively complete, which is suitable for the characterization of the TSV / TGV through hole morphology.

[0040] It should be noted that the laser of the present invention is a laser that can cause the wafer material of the cutting path to generate local high temperature, preferably a short-pulse high-energy laser, and more preferably an infrared laser. The laser of the present invention can cause the silicon or glass material to undergo a phase change (such as from a crystalline state to an amorphous state) or form a tiny void structure through local high temperature, thereby constructing a weakened "invisible layer". After the invisible layer is formed along the set cutting path, appropriate mechanical force or thermal stress is applied to the substrate to cause cracks in the layer along the path, smoothly splitting the wafer or glass substrate into the desired fragments. Then, the internal morphology of TSV / TGV can be accurately observed using a scanning electron microscope or a metallographic microscope. Therefore, compared with methods such as FIB, 3DXray, slicing, and polishing machines, the characterization method of the present invention has the advantage of more accurate cutting position.

[0041] It should be noted that the material of the interposer wafer may be a silicon substrate or a glass substrate, the through hole may be a hole that penetrates the interposer obtained by etching in the interposer wafer, and one through hole or multiple through holes may be etched on one interposer wafer. An insulating layer may be deposited on the inner wall of the through hole, and the material of the insulating layer may be at least one of aluminum oxide and silicon oxide, and a metal layer may also be deposited on the surface of the insulating layer, that is, the through hole mentioned in the present invention may be a through hole without a deposit, or a through hole with a plurality of layers of material deposited.

[0042] In some embodiments of the present invention, step S20 includes: focusing the laser beam to one end of the cutting path of the interposer wafer, and moving along the cutting path to the other end. That is, the irradiation direction of the laser beam can be along the depth of the through hole. At this time, the cutting path can be along the diameter direction of the through hole, and the laser beam moves from one side of the through hole to the other side of the through hole for cutting. This cutting method has the advantages of more accurate cutting position, smaller damaged area, and faster cutting speed.

[0043] In some embodiments of the present invention, the power of the laser beam is less than 1 W. The power of the laser beam can be 0.8 W, 0.5 W or 0.3 W. The power within the above range can ensure that the irradiated area of ​​the interposer wafer can form a modified area quickly.

[0044] In some embodiments of the present invention, the moving speed of the laser beam is A, 0<A<1000mm / s. The moving speed of the laser beam can be 40mm / s, 800mm / s or 1000mm / s. The moving speed within the above range can ensure that the path passed by the laser can form a better modified area, with more modified points and cracks, which is convenient for the intermediate layer wafer to break. If the moving speed of the laser beam is too fast, the laser beam will stay in the focus position for a short time, the concentrated energy is insufficient, and the temperature does not meet the requirements for forming the modified area.

[0045] In some embodiments of the present invention, the diameter of the modified point is less than 5 μm. The diameter of the modified point can be 4 μm, 3 μm, 2 μm or 1 μm. If the diameter of the modified point is greater than 5 μm, the cutting accuracy will be reduced and the internal morphology of the through-hole structure cannot be specifically observed.

[0046] In some embodiments of the present invention, the material of the interposer wafer includes a glass substrate, and step S30 includes: applying mechanical stress on the cutting route to increase the cracks in the modified region until the glass substrate breaks.

[0047] In the technical solution of the present invention, when the material of the interposer wafer is a silicon substrate, the modified area will be directly broken to obtain the cut interposer wafer. When the material of the interposer wafer is a glass substrate, in step S30, it is necessary to apply mechanical stress on the cutting route to increase the cracks in the modified area of ​​the glass substrate, making it easy to break. The purpose of applying mechanical stress is to gradually release the stress inside the glass substrate, thereby breaking the glass substrate.

[0048] In some embodiments of the present invention, the method of applying mechanical stress includes lifting a film expander. Applying mechanical stress by the above method can cause the glass substrate to break faster along the modified area.

[0049] In some embodiments of the present invention, the method of applying mechanical stress includes lifting a film expander, and the height of the film expander is 20 to 50 μm. The height of the film expander can be 20 μm, 40 μm or 50 μm. The height of the lift within the above range can ensure that the applied stress is small, thereby guiding the cracks in the modified area to expand more evenly. This controlled stress effect makes the cutting edge smoother and reduces burrs. The lifting height is mainly adjusted by using the grain spacing after film expansion as a measure.

[0050] In some embodiments of the present invention, step S40 includes: observing the internal structure of the through hole in the cut interposer wafer by scanning electron microscope. That is, the cross section of the cut interposer wafer can be pasted on a glass slide with conductive adhesive and observed by scanning electron microscope. The steps of selecting scanning electron microscope for observation are fewer, more convenient, and lower in cost.

[0051] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0052] Example 1

[0053] A method for characterizing the internal structure of a through hole in a chip, wherein the chip is a silicon substrate with a through hole of 21.53 μm in diameter and 103.1 μm in depth, comprising the following steps:

[0054] S10, setting a cutting path on the silicon substrate, wherein the cutting path is along the diameter direction of the through hole;

[0055] S20-S30, focusing a 0.8W laser beam irradiated along the depth direction of the through hole onto the cutting path, with an irradiation time of 5e-7s and a moving speed of 600mm / s, to obtain a modified area, wherein a modified point and a crack are formed in the modified area, wherein the diameter of the modified point is 2μm; after the laser beam irradiation is completed, the silicon substrate is broken into two parts along the cutting path;

[0056] S30, sticking the cut surface of the cut silicon substrate onto a glass slide with conductive glue, and moving it to a scanning electron microscope to observe the internal structure of the through hole.

[0057] Example 2

[0058] The chip of this embodiment is a silicon substrate with a through hole of 20.47 μm in diameter and 101.0 μm in depth. A layer of aluminum oxide film is grown inside the through hole as an insulating layer. The characterization method thereof is different from that of Embodiment 1 in that:

[0059] The laser beam power is 0.8W, the irradiation time is 7e-7s, the moving speed is 600mm / s, and the modified spot diameter is 3μm.

[0060] Example 3

[0061] The chip of this embodiment is a silicon substrate with a through hole of 21.77 μm in diameter and 101.6 μm in depth. A layer of silicon oxide film is grown inside the through hole as an insulating layer. The characterization method thereof is different from that of Embodiment 1 in that:

[0062] The laser beam power is 0.8W, the irradiation time is 6e-7s, the moving speed is 600mm / s, and the modified spot diameter is 3μm.

[0063] Example 4

[0064] The chip of this embodiment is a glass substrate with a through hole of 52.09 μm in diameter and 505.0 μm in depth. The characterization method thereof is different from that of Embodiment 1 in that:

[0065] The laser beam power is 0.8W, the irradiation time is 1e-6s, the moving speed is 600mm / s, and the modified spot diameter is 3μm.

[0066] Comparative Example 1

[0067] The chip of this comparative example is a silicon substrate with a through hole of 11.50 μm in diameter and 80 μm in depth, and its characterization method comprises the following steps:

[0068] First, use FIB to dig out part of one side of the through hole for half an hour, and then use scanning electron microscope to observe the internal structure of the through hole. The FIB parameters are: the ion beam is a liquid Ga ion source, the acceleration voltage is 0.5kV~30kV, the beam current intensity is 0.6pA~65nA, and the working distance with the electron beam intersection is 7.0mm.

[0069] Comparative Example 2

[0070] The chip of this comparative example is a silicon substrate with a square groove with a side length of 200 μm, comprising the following steps:

[0071] The sample was first polished with a grinder and polisher, and then the sidewall morphology of the etched square groove was observed using a metallographic microscope.

[0072] Comparative Example 3

[0073] The chip of this comparative example is a glass substrate with a through hole of 50 μm in diameter and 500 μm in depth, and comprises the following steps:

[0074] First, the sample was polished with a grinder and polisher, and then the sidewall morphology of the etched square groove was observed with a metallographic microscope. The specific operation of the grinder and polisher is as follows: open the turntable with sandpaper, rotate the turntable at a speed of 400 revolutions per second, and then hold the sample for polishing.

[0075] Performance Testing

[0076] The internal structures observed in Examples 1 to 4 and Comparative Examples 1 to 3 are as follows: Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 and Figure 7 shown.

[0077] Depend on Figure 1 It can be seen that the cut sample is a silicon substrate with TSVs of 21.53μm diameter and 103.1μm depth. The blind holes are first cut by laser hidden cutting and the side wall morphology of the sample is observed by SEM.

[0078] Depend on Figure 2 It can be seen that the cut sample is a silicon substrate with a TSV of 20.47μm diameter and 101.0μm depth and a layer of aluminum oxide film is grown as an insulating layer. The blind hole is first cut by laser hidden cutting and the side wall morphology of the sample is observed by SEM.

[0079] Depend on Figure 3 It can be seen that the cut sample is a silicon substrate with a TSV of 21.77μm diameter and 101.6μm depth and a layer of silicon oxide film is grown as an insulating layer. The blind hole is first cut by laser hidden cutting and the side wall morphology of the sample is observed by SEM.

[0080] Depend on Figure 4 It can be seen that the cut sample is a glass substrate with a TGV of 52.09μm diameter and 505.0μm depth. The through hole is first cut by laser hidden cutting, and then the surface of the sample to be observed is gold plated by an ion sputtering instrument. Finally, the side wall morphology of the sample is observed by SEM.

[0081] FIB is slow to dig, has limited cutting range and is very expensive. FIB also has the consequence of filling the through hole, due to Figure 5 It can be seen that the diameter of the TSV opening is shrinking;

[0082] Depend on Figure 6 It can be seen that the sample is a silicon substrate with a square groove with a side length of 200 μm; Figure 7 It can be seen that the sample is a glass substrate with a 50μm diameter TGV. Although the grinder and polisher speeds up the sample characterization, the grinder and polisher requires the sample to be immersed in AB glue and condensed into a block with a grinder. Therefore, the sample polished by the grinder and polisher cannot continue to be observed under the SEM. The results of observation under the metallographic microscope show that the polished sample is rough on both sides. The grinding speed of the grinder and polisher is uncontrollable, and it is easy to over-grind and damage the sample structure.

[0083] In summary, the present invention combines laser cutting technology with scanning electron microscopy technology to obtain a method for characterizing the internal structure of chip through-holes. Other characterization methods such as FIB or polishing machines are difficult to achieve high efficiency, high accuracy and low cost characterization of the internal structure of chip through-holes. The method obtained by the present invention can effectively shorten the time of TSV / TGV characterization and control the cost required for TSV / TGV characterization. The laser cutting technology can effectively, reliably, quickly and economically cut the TSV / TGV from the opening, and the surface is smooth and clean, and then the scanning electron microscope technology is used to observe the inner wall morphology of the TSV / TGV. This method can be widely used in the design and production of TSV / TGV in the future to evaluate the feasibility of new insulating layers, diffusion barrier layers and seed layers.

[0084] The above are only preferred embodiments of the present invention, and do not limit the patent scope of the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the patent protection scope of the present invention.

Claims

1. A method for characterizing the internal structure of a through hole in a chip, characterized in that: The chip includes an interposer wafer, the interposer wafer is provided with a through hole penetrating the interposer, and the method for characterizing the internal structure of the through hole in the chip includes the following steps: S10, providing an interposer wafer, and setting a cutting path on the interposer wafer, wherein the cutting path passes through at least one of the through holes; S20, focusing the laser beam onto the cutting path of the interposer wafer, so that the temperature of the wafer material on the cutting path increases and sublimates under the irradiation of the light beam, thereby obtaining a modified region, wherein the modified region is formed with modified points and cracks; S30, breaking the interposer wafer along the cutting path to obtain a cut interposer wafer; S40, observing the internal structure of the through hole in the cut interposer wafer.

2. The method for characterizing the internal structure of a through hole in a chip according to claim 1, characterized in that: Step S20 includes: focusing the laser beam to one end of a cutting path of the interposer wafer, and moving the laser beam to the other end along the cutting path.

3. The method for characterizing the internal structure of a through hole in a chip according to claim 2, characterized in that: The power of the laser beam is less than 1W.

4. The method for characterizing the internal structure of a through hole in a chip according to claim 2, characterized in that: The moving speed of the laser beam is A, 0<A<1000mm / s.

5. The method for characterizing the internal structure of a through hole in a chip according to claim 1, characterized in that: The diameter of the modified point is less than 5 μm.

6. The method for characterizing the internal structure of a through hole in a chip according to claim 1, characterized in that: The material of the interposer wafer includes a glass substrate, and step S30 includes: Mechanical stress is applied to the cutting route to increase the cracks in the modified region until the glass substrate breaks.

7. The method for characterizing the internal structure of a through hole in a chip according to claim 6, characterized in that: The method of applying mechanical stress includes lifting the film expander.

8. The method for characterizing the internal structure of a through hole in a chip according to claim 7, characterized in that: The method of applying mechanical stress includes lifting a film spreader, and the height of the film spreader lifting is 20 to 50 μm.

9. The method for characterizing the internal structure of a through hole in a chip according to claim 1, characterized in that: Step S40 includes: observing the internal structure of the through hole in the cut interposer wafer by means of a scanning electron microscope.

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