A wafer thinning device

Abstract

The present invention relates to the technical field of wafer thickness reduction, and discloses a wafer thinning device, which includes a power supply and a tool electrode. One pole of the power supply is electrically connected to the tool electrode, and the other pole of the power supply can be electrically connected to the wafer to be processed. A plurality of discharge terminals are provided on the tool electrode. The present invention utilizes the principle of electric discharge machining. By connecting the tool electrode and the wafer to the two poles of the power supply respectively, and then relying on the voltage to break down the gap between the tool electrode and the wafer, a discharge channel is formed between the tool electrode and the wafer, and then the surface of the wafer at the position of the discharge channel is thinned. The whole process belongs to non-contact machining, there is no contact force between the tool electrode and the wafer, and there is no risk of the wafer being broken due to excessive contact force.

Description

Technical Field

[0001] The present invention relates to the technical field of wafer thinning, and particularly to a wafer thinning device. Background Art

[0002] A wafer is a sheet-shaped semiconductor and an essential material for manufacturing integrated circuits. Its manufacturing process mainly includes three stages: ingot manufacturing, wafer preparation, and wafer finishing.

[0003] Ingot manufacturing: The first process of wafer manufacturing is ingot manufacturing. Generally, it is obtained by purifying the raw material → melting / vaporizing → crystallizing to get an initial ingot. Subsequently, the outer surface of the ingot is ground and finished by external cylindrical grinding to complete the manufacturing of an ingot.

[0004] Wafer preparation: A wafer is a circular sheet-shaped wafer cut uniformly from an ingot. After the ingot is prepared, the ingot is sliced into wafers with uniform thickness by wire sawing or electrical discharge wire / wafer slicing, which are called sliced wafers.

[0005] Wafer finishing: The surface quality and thickness of the wafer after preparation do not meet the requirements for etching circuits and manufacturing integrated circuit devices. Therefore, it is necessary to correct the surface quality and wafer thickness in the wafer finishing part. The main processes include: grinding, lapping, polishing, and chemical mechanical polishing. Specifically, first, the diamond tool grinding process is used to efficiently remove the surface cracks generated by the slicing process. Lapping is a mechanical non-abrasive processing technology that can remove the surface roughness and part of the subsurface damage of the sliced wafer. Usually, after the lapping process, initial global planarization can be achieved. Chemical mechanical polishing (CMP) is usually the standard process to achieve a large flat surface without damage and is the last process of wafer finishing.

[0006] Wafer thinning refers to the process of further reducing the thickness of the sliced wafer to the designed range. By reducing the thickness of the wafer, components with smaller thickness are manufactured. The main purposes are to reduce the packaging volume of the integrated circuit, improve the electrical performance of the device, and enhance the heat dissipation of the device. Since the sliced wafer is cut from the ingot by a diamond wire saw, there are inevitably defects such as cracks and warping on the cutting surface. On the other hand, it is difficult to ensure that the cutting surface is completely flat during the cutting process, and the thickness of the wafer is uneven. Therefore, thinning also plays a role in planarizing the wafer surface.

[0007] With the progress of electronic science and technology, all industries are developing towards automation and intelligence, thus increasing the demand for the number of integrated circuit electronic devices in the market. To meet the sharp growth demand for electronic market devices, the wafer size is continuously increased to improve the output of electronic devices and reduce the manufacturing cost of electronic devices. However, in order to increase the mechanical strength of the wafer and prevent cracks or breakage of the wafer during the preparation process due to handling, loading and unloading, and processing, the thickness of the wafer will also increase correspondingly while the wafer size increases. On the contrary, the current market for electronic devices is constantly developing towards smaller, lighter and thinner directions. For example, the thickness of new smartphones and laptops is within 10 mm. At the same time, electronic devices are also developing towards system integration and 3C (Computer, Communication, Consumer electronic) integration, which promotes the reform of chip packaging technology in the post-Moore era. The three-dimensional packaging technology based on TSV (Through-Silicon Via) has become the mainstream of future packaging technology due to its small space occupation, high integration and excellent electrical performance. Since the three-dimensional packaging technology based on TSV (Through-Silicon Via) is achieved by stacking multiple chips and relying on through-silicon vias for electrical connection, it reduces the packaging area and shortens the distance of electrical connection between modules in the integrated circuit to achieve better electrical performance. However, limited by the current manufacturing process of through-silicon vias, the aspect ratio of through-silicon vias can generally only reach 10-15. To improve the surface utilization rate of the wafer, the diameter of the through-silicon via should be reduced as much as possible. Therefore, the three-dimensional packaging technology puts forward certain requirements for the thickness of the wafer. Moreover, the thinning of the wafer not only helps to manufacture smaller and thinner devices, improves the heat dissipation effect while reducing the weight, but also further shortens the distance of electrical connection between modules in the integrated circuit, and at the same time improves the integration and performance of the device. In addition, for current SiC power devices, taking MOSFET devices as an example, the thinning of the SiC substrate can reduce the on-resistance of the device, reduce unnecessary on-voltage drop, and improve the performance of power devices in high-voltage environments.

[0008] All in all, wafer thinning is a very necessary and important process in the wafer manufacturing process, and it is also a key process to improve the performance of devices in all aspects.

[0009] Due to the very high brittleness and chemical stability of the third-generation semiconductors, the traditional methods for processing silicon wafers are difficult to be applied to the processing of SiC wafers with high efficiency, high quality and low cost. Therefore, the application object of this system is mainly the third-generation semiconductor wafers, and it can also be generally used for the wafer manufacturing of other semiconductor materials.

[0010] In the traditional wafer thinning process, grinding wheels are generally used for thinning. The wafer is thinned layer by layer by rotating and grinding the grinding wheel on the wafer surface. However, existing common semiconductor materials, such as silicon, gallium arsenide, silicon carbide, gallium nitride, etc., are hard and brittle, belonging to typical difficult-to-machine materials. Correspondingly, when thinning the wafer, the wafer is prone to breakage under the action of mechanical stress, especially when processing large-diameter wafers. Therefore, a wafer thinning device is needed to solve the problem of wafer breakage caused by mechanical stress in the traditional wafer thinning process. Summary of the Invention

[0011] In order to overcome the deficiencies of the prior art, the present invention provides a wafer thinning device, which solves the problem of wafer breakage caused by mechanical stress in the traditional wafer thinning process.

[0012] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0013] A wafer thinning device is provided, including a power supply and a tool electrode. One pole of the power supply is electrically connected to the tool electrode, and the other pole of the power supply can be electrically connected to the wafer to be processed. A plurality of discharge terminals are provided on the tool electrode.

[0014] As a further improvement of the above technical solution, the tool electrode includes a main body, and a plurality of the discharge terminals are uniformly arrayed outside the main body.

[0015] As a further improvement of the above technical solution, an insulating layer is provided between the discharge terminal and the main body, and a plurality of capacitors are provided on the main body.

[0016] As a further improvement of the above technical solution, the main body includes a circular base plate. A plurality of capacitor grooves are provided in the circular base plate to install capacitors. A plurality of protrusions protrude outward from the side surface of the circular base plate, and mounting grooves are formed between the protrusions to install the discharge terminals. Different discharge terminals correspond to different capacitors.

[0017] As a further improvement of the above technical solution, a plurality of the discharge terminals are independent of each other. When the power supply discharges, a plurality of the discharge terminals respectively discharge to the wafer to be processed.

[0018] As a further improvement of the above technical solution, the power supply is a pulse power supply, and when the power supply performs a single pulse discharge, each of the discharge terminals discharges to the wafer.

[0019] As a further improvement of the above technical solution, the tool electrode can rotate relative to the wafer, and the axial distance between the tool electrode and the wafer is adjustable.

[0020] As a further improvement of the above technical solution, a container for storing an insulating liquid is further provided, the tool electrode and the wafer are placed in the container, the insulating liquid is one or more of kerosene, mineral oil or deionized water, and particles for improving the discharge state are dispersed in the insulating liquid.

[0021] As a further improvement of the above technical solution, the tool electrode and the wafer are immersed in the insulating liquid; or the insulating liquid flows through a supply pipe to the surface of the wafer so that the insulating liquid fills the gap between the tool electrode and the surface of the wafer.

[0022] As a further improvement of the above technical solution, gaps are left between the discharge terminals.

[0023] The beneficial effects of the present invention are as follows: The present invention utilizes the principle of electric discharge machining. By connecting the tool electrode and the wafer to the two poles of the power supply respectively, and then relying on the voltage to break down the gap between the tool electrode and the wafer, a discharge channel is formed between the tool electrode and the wafer, and then the surface of the wafer at the position of the discharge channel is thinned. Since the discharge channel always occurs between the two closest points between the tool electrode and the wafer, and the energy of the discharge channel is concentrated and the cross-section is small, the surface of the wafer can be uniformly thinned after multiple discharges, and the whole process belongs to non-contact machining. There is no contact force between the tool electrode and the wafer, and there is no risk of the wafer being broken due to excessive contact force. Description of the Drawings

[0024] The present invention will be further described below in conjunction with the drawings and embodiments.

[0025] Figure 1 is a working schematic diagram of a wafer thinning device in an embodiment of the present invention;

[0026] Figure 2 is a schematic diagram of the working principle of a wafer thinning device in an embodiment of the present invention;

[0027] Figure 3 is a working schematic diagram of a wafer thinning device in an embodiment of the present invention;

[0028] Figure 4 is a three-dimensional schematic diagram of a working electrode in an embodiment of the present invention. Detailed Description of the Embodiments

[0029] This part will describe the specific embodiments of the present invention in detail. The preferred embodiments of the present invention are shown in the drawings. The function of the drawings is to supplement the description of the text part of the specification, so as to be able to intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it cannot be understood as a limitation on the protection scope of the present invention.

[0030] In the description of the present invention, if orientation descriptions are involved, such as "upper", "lower", "front", "rear", "left", "right", etc., the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the drawings. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. When a certain feature is referred to as "arranged", "fixed", "connected" to another feature, it can be directly arranged, fixed, connected to another feature, or indirectly arranged, fixed, connected to another feature.

[0031] In the description of the present invention, if "several" is involved, its meaning is one or more; if "multiple" is involved, its meaning is more than two; if "greater than", "less than", "exceeding" are involved, they should all be understood as not including the recited number; if "above", "below", "within" are involved, they should all be understood as including the recited number. If "first", "second" are involved, they should be understood as being used to distinguish technical features, rather than indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or the sequence relationship of the indicated technical features.

[0032] In addition, unless otherwise defined, the technical terms and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention pertains. The terms used in the present invention are only for describing specific embodiments, rather than limiting the present invention.

[0033] Referring to Figure 1 , a working schematic diagram of a wafer thinning device in the prior art is shown. In the prior art, mechanical grinding is used for wafer thinning. In the figure, the wafer 1 is located in the wafer tray 2, the grinding wheel 3 contacts the surface of the wafer 1 and rotates relative to the wafer 1, and the diamond abrasive grains 31 on the grinding wheel 3 contact and grind the surface of the wafer 1. Here, a relatively large contact force is applied to the surface of the wafer 1 by the diamond abrasive grains 31. Since the wafer is a brittle material, the grinding of the wafer 1 by the diamond abrasive grains 31 is likely to cause the wafer 1 to break, especially when the diameter of the wafer 1 is larger, the possibility of its being broken by force is greater (that is, the maximum contact force it can withstand is smaller).

[0034] In addition, since the surface roughness of the wafer manufactured by grinding is relatively high, generally, in order to obtain a better processed surface, finer diamond particles need to be replaced. However, the thinning of the abrasive grains will cause a significant increase in the cost of the grinding wheel. And since grinding is the contact movement of the abrasive grains on the wafer surface, in order to achieve a better wafer surface effect, generally, long-term grinding is required to ensure that the abrasive grains contact all positions on the wafer surface.

[0035] Based on this, the solution in the present application adopts a non-contact processing technology to process and thin the surface of the wafer, avoiding the influence of mechanical stress on the wafer during the thinning process, thereby avoiding the situation where the wafer breaks due to contact force.

[0036] Referring to Figure 2 , a schematic diagram of the working principle of a wafer thinning device in an embodiment of the present invention is shown. The wafer 1 is used as one pole of the power supply 4 (or electrically connected to a certain pole of the power supply), and the other pole of the power supply 4 is connected to a tool electrode 5. There is a gap between the tool electrode 5 and the wafer 1. When a pulsed voltage is applied between the two poles, the closest point between the poles is broken down under the current conditions, forming a discharge channel. Since the cross-sectional area of the channel is very small and the discharge time is extremely short, the energy is highly concentrated (10 - 107 W / mm), and the instantaneous high temperature generated in the discharge area is sufficient to melt or even evaporate the material, resulting in the formation of a small pit. After the first pulsed discharge ends, after a very short interval, the second pulse breaks down and discharges at the closest point between the other poles. When there are enough pits, the wafer is thinned.

[0037] To achieve a better thinning effect, the tool electrode 5 includes a plurality of discharge terminals, and the discharge terminals are evenly distributed in a certain area to achieve synchronous and uniform processing of the wafer part in this area.

[0038] Referring to Figure 3 , a working schematic diagram of a wafer thinning device in an embodiment of the invention is shown. The wafer 1 is placed on a rotatable workbench 6, enabling the wafer 1 to rotate around its central axis. The tool electrode 5 is driven by a transmission shaft located at the upper part of the device and can rotate around the central axis of the tool electrode 5.

[0039] The rotation directions of the wafer 1 and the tool electrode 5 are opposite. Therefore, the discharge terminals on the tool electrode 5 can discharge to multiple surface areas of the wafer 1.

[0040] Since the distance between the surface of the wafer 1 and the discharge terminals of the tool electrode 5 becomes larger after the wafer 1 is thinned, to maintain a good processing effect, the tool electrode 5 moves towards the wafer 1 to ensure that the gap between the discharge terminals of the tool electrode 5 and the wafer 1 is maintained within a suitable range (preferably 0.01 - 0.05 mm).

[0041] Furthermore, the wafer 1 and the tool electrode 5 are jointly placed in a liquid medium with a certain insulation degree (commonly kerosene or mineral oil or deionized water), reducing the voltage intensity requirement for the required breakdown voltage and facilitating the removal of debris generated during thinning.

[0042] Furthermore, adding fine particles 7 such as carbon powder, silicon powder, copper powder, or diamond nanoparticles into the liquid medium can improve the stability of the discharge state, improve the surface quality, and increase the processing efficiency, ultimately achieving high-efficiency and high-quality wafer thinning.

[0043] Referring to Figure 4 , a three-dimensional schematic diagram of the working electrode in an embodiment of the invention is shown. The working electrode has the main shaft 51 that can be fixed on the connecting shaft as its self-rotating axis. The working electrode includes a main body, and the main body includes a circular base plate located on the main shaft 51. A number of capacitor grooves 54 are provided in the circular base plate to install capacitors. A number of protrusions protrude outward from the side surface of the circular base plate, and mounting grooves are formed between the protrusions to mount the discharge terminals 52. Different discharge terminals 52 are correspondingly connected to different capacitors.

[0044] Correspondingly, in a specific embodiment, the discharge terminal 52 is selected as a copper block as the metal electrode. The metal electrode can also be selected as a conductive solid such as graphite or a silver block. The discharge terminals 52 are distributed in a circular array on the periphery of the working electrode, and a certain gap is left between the discharge terminals 52, aiming to facilitate the flow of the working fluid and chip removal (such as waste chips generated during thinning). An insulating layer 53 is provided between the discharge terminal 52 and the main body of the working electrode to make each discharge terminal independent of each other.

[0045] Therefore, based on the structure of this working electrode, during wafer thinning, the discharge pulse charges each capacitor simultaneously. The discharge terminals connected to each capacitor break down the liquid medium at the nearest point between the electrodes under the current conditions, forming a discharge channel. Therefore, when using this working electrode, different from the traditional pulsed discharge, the number of discharges formed during a power pulse process depends on the number of discharge terminals. The reason is that when inter-electrode discharge occurs in one electrode block, it does not affect other parallel circuits. Therefore, multiple inter-electrode discharges can be achieved during one pulse process, thereby improving the discharge efficiency.

[0046] In another embodiment of the present invention, the wafer thinning device includes a supply pipe, and the insulating liquid flows through the supply pipe to the surface of the wafer. The insulating liquid fills the gap between the tool electrode and the wafer surface, achieving the same technical effect as the solution of immersing the tool electrode and the wafer in the insulating liquid.

[0047] The above is a specific description of the preferred embodiments of the present invention, but the present invention is not limited to the described embodiments. Those skilled in the art can also make various equivalent deformations or substitutions without departing from the purpose of the present invention. In addition, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

Claims

1. A wafer thinning device, characterized in that, it includes a power supply and a tool electrode. One pole of the power supply is electrically connected to the tool electrode, and the other pole of the power supply can be electrically connected to the wafer to be processed. The tool electrode is provided with a plurality of discharge terminals. The tool electrode includes a main body, and a plurality of the discharge terminals are uniformly arrayed outside the main body. The main body includes a circular base plate located on the main shaft. The tool electrode takes the main shaft fixed on the connecting shaft as its self-rotation axis. A plurality of capacitor grooves are arranged in the circular base plate to install capacitors. The side surface of the circular base plate protrudes outward to form a plurality of protrusions, and mounting grooves are formed between the protrusions to install the discharge terminals. The discharge terminals are distributed in a circular array on the periphery of the tool electrode. Different discharge terminals correspond to different capacitors. The power supply is connected in series with the capacitor, and the capacitor is connected in series with the discharge terminal. The tool electrode can rotate relative to the wafer. The plurality of discharge terminals are independent of each other. When the power supply discharges, the plurality of discharge terminals respectively discharge to the wafer to be processed.

2. The wafer thinning device according to claim 1, characterized in that, an insulating layer is provided between the discharge terminal and the main body, and a plurality of capacitors are provided on the main body.

3. The wafer thinning device according to claim 1, characterized in that, the power supply is a pulse power supply, and when the power supply performs a single pulse discharge, each discharge terminal discharges to the wafer.

4. The wafer thinning device according to claim 1, characterized in that, the axial distance between the tool electrode and the wafer is adjustable.

5. The wafer thinning device according to claim 4, characterized in that, a container for storing an insulating liquid is further provided. The tool electrode and the wafer are placed in the container. The insulating liquid is one or more of kerosene, mineral oil or deionized water. Particles for improving the discharge state are dispersed in the insulating liquid.

6. The wafer thinning device according to claim 5, characterized in that, the tool electrode and the wafer are immersed in the insulating liquid; or the insulating liquid flows to the surface of the wafer through a supply pipe so that the insulating liquid fills the gap between the tool electrode and the surface of the wafer.

7. The wafer thinning device according to claim 4, characterized in that, gaps are left between the discharge terminals.

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