Grinding method and corresponding wafer structure

Abstract

The invention relates to the field of semiconductor packaging, and provides a grinding method and a corresponding wafer structure. Comprising the steps that a wafer is provided, the wafer is provided with a plurality of through holes, the wafer is provided with a plurality of conduction columns, and each conduction column fills the corresponding through hole; sequentially using at least one soft grinding pad and applying corresponding rotating speed and pressure to perform primary grinding on the conduction columns, so that the heights of the multiple conduction columns are consistent; and sequentially using corresponding grinding pads and applying corresponding rotating speed and pressure to carry out secondary grinding on the conducting column subjected to primary grinding, so that the conducting column subjected to secondary grinding is consistent with the surface of the wafer in height. Therefore, a good foundation is laid for the subsequent formal process, and the improvement of the process effect and the optimization of the product quality are ensured.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor packaging and discloses a grinding method and a corresponding wafer structure. Background Art

[0002] The traditional backside exposure (BVR) technology of through-holes has problems such as tilting and fracture of conductive pillars during the chemical mechanical polishing (CMP) process. At present, the chemical mechanical polishing process mainly uses a polishing liquid that has a grinding effect on the conductive pillars for chemical mechanical polishing. However, due to the limited capacity of the front-end process, there are differences in the height of the conductive pillars on the surface of the wafer when it reaches the chemical mechanical polishing process. For example, it is usually manifested as high at the edge and low in the center; and the outer circle linear speed of the chemical mechanical polishing process is relatively large, which makes the edge of the wafer subject to greater force. Combining the above two weak links, the chemical mechanical polishing process is prone to cause the conductive pillar to tilt. This will have a certain impact on the subsequent process links and product quality. Summary of the invention

[0003] The purpose of the present invention is to solve the problem that the existing grinding process may cause the conductive pillar to tilt, thereby affecting the subsequent process, and provide a grinding method and a corresponding wafer structure. In order to achieve the above object, the present invention provides a grinding method, comprising: Providing a wafer, wherein the wafer has a plurality of through holes, the wafer has a plurality of conductive pillars, and each of the conductive pillars fills the corresponding through hole; Using at least one soft grinding pad and applying a corresponding rotation speed and pressure to grind the conductive pillars once, so that the heights of the plurality of conductive pillars are consistent; The conductive pillars after the first grinding are ground for a second time by using corresponding grinding pads in sequence and applying corresponding rotation speeds and pressures, so that the height of the conductive pillars after the second grinding is consistent with that of the wafer surface.

[0004] As an implementation method, the rotation speed and pressure at the corresponding position applied each time the corresponding grinding pad is used to grind the wafer during the first grinding are smaller than the rotation speed and pressure at the corresponding position applied each time the corresponding grinding pad is used to grind the wafer during the second grinding.

[0005] As an implementable embodiment, the grinding liquid flow rate when a soft grinding pad is used to grind the wafer each time during the first grinding is less than the grinding liquid flow rate when a corresponding grinding pad is used to grind the wafer each time during the second grinding, and the grinding time when a soft grinding pad is used to grind the wafer each time during the first grinding is greater than the grinding time when a corresponding grinding pad is used to grind the wafer each time during the second grinding.

[0006] As an implementation method, the wafer surface also has a silicon oxide layer, the silicon oxide layer surface also has a silicon nitride layer, and the conductive pillar and the wafer surface are highly consistent, including that the conductive pillar and the silicon nitride layer surface on the wafer are highly consistent.

[0007] As an implementation method, the at least one soft grinding pad is used in sequence and a corresponding rotation speed and pressure are applied to grind the conductive pillar once, which includes: The soft polishing pad and the soft polishing pad are used sequentially and a corresponding rotation speed and pressure are applied to each soft polishing pad to grind the conductive column once.

[0008] As an implementation method, the rotation speed applied each time the soft polishing pad is used for grinding is the same, and pressure is applied to multiple areas from the inside to the outside of the wafer each time the soft polishing pad is used for grinding, and the pressure applied to different areas is adjusted according to the height of the conductive column at the corresponding position.

[0009] As an implementable embodiment, before one grinding, the height of the conductive pillars in the edge area of ​​the wafer surface is greater than that in other areas, and during one grinding, the pressure applied to the edge area of ​​the wafer surface is greater than that applied to other areas.

[0010] As an implementable method, using a corresponding polishing pad and applying a corresponding rotation speed and pressure to perform a second polishing on the conductive pillar after the first polishing includes: The conductive column after the first grinding is secondarily ground using a soft grinding pad, a hard grinding pad, a hard grinding pad, and a soft grinding pad in sequence and applying corresponding rotation speeds and pressures.

[0011] As an implementation method, the rotation speed and pressure applied when using different grinding pads for secondary grinding are the same, and each time the wafer is ground using the corresponding grinding pad, the pressure applied to the edge area of ​​the wafer surface is greater than the pressure applied to other areas.

[0012] As an implementable embodiment, the applied rotation speed is a relative rotation speed formed on the wafer by rotating the grinding head and the grinding pad, and the applied pressure is a corresponding pressure formed by the grinding head on different areas of the wafer from the inside to the outside.

[0013] Correspondingly, the present invention also provides a wafer structure formed according to the above-mentioned grinding method, comprising: a wafer having a plurality of through holes, wherein the through holes have conductive pillars, and the heights of the conductive pillars and the surface of the wafer are consistent.

[0014] Beneficial effects of the present invention: When the conductive pillars are of different heights, the present invention adds a soft polishing pad pre-polishing process before the conventional chemical mechanical polishing process, using a low speed and low edge pressure method, the purpose is to grind the conductive pillars flat, so that the conductive pillars on the wafer surface are more evenly stressed when entering the conventional chemical mechanical polishing process. In this process, the chemical corrosion efficiency of the grinding liquid is fully utilized, so that the surface of the conductive pillars can be gradually ground flat and smooth with a consistent height, thereby laying a good foundation for the subsequent formal process, ensuring the improvement of the process effect and the optimization of product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of a wafer before grinding provided by some embodiments of the present invention; Figure 2 A schematic diagram of a conductive pillar tilted according to some embodiments of the present invention; Figure 3 A schematic diagram of a conductive pillar being broken according to some embodiments of the present invention; Figure 4 and Figure 5 A schematic diagram of the gradual corrosion of a conductive pillar in a wafer through hole during a grinding process provided by some embodiments of the present invention; Figure 6 Electron microscope images of tilted conductive pillars provided in some embodiments of the present invention; Figure 7 An electron microscope image of a fractured conductive column provided in some embodiments of the present invention; Figure 8 A schematic diagram of a conductive column after a grinding process according to some embodiments of the present invention; Fig. 9 A schematic diagram of a conductive column after secondary grinding provided by some embodiments of the present invention; Fig.10 A schematic diagram of area division for applying pressure to different areas of a wafer from the inside to the outside, provided in some embodiments of the present invention; Fig.11 Electron microscope images of conductive pillars without abnormal morphology provided in some embodiments of the present invention. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0018] For ease of description, spatially relative terms such as "under", "below", "below", "above", "on", "upper", etc. may be used herein to describe the relationship of an element or feature to other elements or features as shown in the drawings. It should be understood that the spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation shown in the drawings. For example, if the device in the drawings is turned over, the elements described as being "under" or "beneath" other elements or features will be oriented "above" the other elements or features. Therefore, the term "under" can include both above and below orientations.

[0019] In some embodiments, the wafer manufacturing process can be broadly divided into two links: the front-end and the back-end of the wafer. The front-end process is carried out in the wafer factory, which is mainly responsible for the processing and manufacturing of the wafer; the back-end process is carried out in the packaging and testing plant, which is mainly responsible for the packaging and testing of the chip. Among them, the chemical mechanical polishing process (CMP) is the key process to achieve global planarization of the wafer. It refers to the synergistic effect of chemical corrosion and mechanical polishing to achieve efficient removal of excess material on the wafer surface and global nano-level planarization. It is a key process technology required for the front-end processes of advanced integrated circuit manufacturing, advanced packaging and other links. The specific process includes: Step 1: fix the wafer at the bottom of the grinding head, and fix the wafer by vacuum adsorption or mechanical clamping; the grinding pad is placed on the grinding disc; Step 2: the rotating grinding head presses on the rotating grinding pad with a certain pressure, and flowing grinding liquid (composed of submicron or nano abrasive particles and chemical solution) is added between the wafer surface and the grinding pad. The grinding liquid is evenly coated under the transmission of the grinding pad and the action of centrifugal force, forming a liquid film between the wafer and the grinding pad; Step 3: achieve flattening through the alternating process of chemical and mechanical film removal. Among them, the grinding pad is a key component for conveying the grinding slurry. It is used to deliver the abrasive particles in the grinding slurry to the wafer surface and remove by-products. Flattening is achieved because the higher parts on the wafer contact the grinding pad and are removed.

[0020] However, if Figure 1 As shown, due to the limited front-end process capability, the height of the conductive pillars 210 on the surface of the wafer 100 varies when the chemical mechanical polishing process is performed, for example, the edge is usually high and the center is low. Therefore, during the polishing, Figure 2 As shown (corresponding to Figure 6 The electron microscope image taken when the actual structure is tilted) The conductive pillar 210 located at the edge of the wafer 100 will have a tilting problem. If the grinding rate of the machine is relatively fast, the bent part of the conductive pillar 210 will be gradually worn away during the grinding process. At the same time, due to the presence of the grinding fluid, it will penetrate into the worn part, causing corrosion, and finally the following will appear on the surface of the copper pillar: Figure 3 and Figure 4 The defect of the fracture state shown (corresponding to Figure 6 On the contrary, if the grinding rate is slow, although the conductive pillar will not be worn away or corroded and broken due to grinding too fast, the tilt of the conductive pillar will remain on the surface and form corresponding defects; this will have a certain impact on the subsequent process links and product quality.

[0021] Therefore, in order to solve the technical problem, some embodiments of the present invention disclose a grinding method, comprising: See also Figure 1 , providing a wafer 100, wherein the wafer 100 has a plurality of through holes, the wafer 100 has a plurality of conductive pillars 210, and each of the conductive pillars 210 fills the corresponding through hole; Use at least one soft grinding pad in turn and apply corresponding rotation speed and pressure to grind the conductive column once, see Figure 8 , so that the heights of the plurality of conductive pillars 210 are consistent; Use a corresponding grinding pad and apply a corresponding rotation speed and pressure to perform a secondary grinding (conventional grinding) on ​​the conductive pillar 100 after the primary grinding. Fig. 9 (correspond Fig.11 The electron microscope image of the actual structure is taken without abnormal morphology), so that the height of the conductive pillar 210 after the secondary grinding is consistent with the surface of the wafer 100.

[0022] The present invention mainly adds a pre-grinding process of a soft grinding pad before the conventional grinding process. The soft grinding pad is first used to carry out the grinding work. After grinding to a specific height, the conventional grinding process is used to carry out the subsequent grinding. The conventional grinding process uses a soft grinding pad and a hard grinding pad in combination to carry out the grinding work, thereby reducing the risk of the conductive column breaking and significantly improving the automatic optical inspection yield.

[0023] In some embodiments, see Figure 1 , the surfaces of the wafer 100 and the conductive pillar 210 also have a silicon oxide layer 220, and the surface of the silicon oxide layer also has a silicon nitride layer 230. In some embodiments, after secondary grinding, the height of the conductive pillar 210 and the surface of the wafer 100 are consistent, including the surface of the conductive pillar 210 and the surface of the silicon oxide layer 230 on the wafer 100 are consistent. In some embodiments, the height of the conductive pillar 210 and the surface of the wafer 100 can be roughly the same or completely the same.

[0024] In some embodiments, the wafer 100 is a silicon wafer, etc., the through hole is a corresponding through silicon via, etc., and the material of the conductive pillar 210 is metal, specifically, a copper pillar or other metal pillar.

[0025] In some embodiments, when the conductive column 210 is a copper column, the polishing pad used for grinding can be used in combination with a polishing liquid for grinding silicon nitride / silicon oxide / copper. According to the surface morphology structure and hardness, the polishing pad can generally be divided into a hard polishing pad and a soft polishing pad. In some embodiments, the hard polishing pad will achieve the function of carrying the polishing liquid by making countless concave grooves on the surface, so as to meet a higher polishing rate and better uniformity in the polishing process; the soft polishing pad can achieve better surface flattening quality by changing its chemical composition or porous structure to assist in the transmission of the polishing liquid and grinding. In some embodiments, the material of the hard polishing pad can be thermosetting polyurethane TSU or thermoplastic polyurethane TPU, etc., and the material of the soft polishing pad can be porous polyurethane, etc.

[0026] In some embodiments, the applied rotation speed is the relative rotation speed of the wafer formed by rotating the grinding head and the grinding pad respectively, and the applied pressure is the corresponding pressure formed by the grinding head on different areas of the wafer from the inside to the outside, for example, see Fig.10, pressure is applied to multiple areas of the wafer from the inside to the outside, such as area Z5, area Z4, area Z3, area Z2, and area Z1, respectively, wherein area Z1 is the edge area of ​​the wafer surface, and the pressure applied to different areas is adjusted according to the height of the conductive column at the corresponding position. In some embodiments, the rotation speed and the pressure at the corresponding position applied each time the corresponding polishing pad is used to polish the wafer 100 during the first polishing are less than the rotation speed and the pressure at the corresponding position applied each time the corresponding polishing pad is used to polish the wafer 100 during the second polishing, for example, the pressure applied to area Z1 during the first polishing is greater than the pressure applied to area Z1 during the second polishing. In some embodiments, the flow rate of the polishing liquid when the soft polishing pad is used to polish the wafer each time during the first polishing is less than the flow rate of the polishing liquid when the corresponding polishing pad is used to polish the wafer each time during the second polishing, and the polishing time when the soft polishing pad is used to polish the wafer each time during the first polishing is greater than the polishing time when the corresponding polishing pad is used to polish the wafer each time during the second polishing.

[0027] In some embodiments, using at least one soft polishing pad in sequence and applying a corresponding rotation speed and pressure to grind the conductive pillar 210 once includes: using a soft polishing pad, a soft polishing pad in sequence and applying a corresponding rotation speed and pressure to each soft polishing pad to grind the conductive pillar 210 once. In some embodiments, the rotation speed applied each time the soft polishing pad is used for grinding is the same, and pressure is applied to different areas of the wafer 100 from the inside to the outside each time the soft polishing pad is used for grinding, and the applied pressure is adjusted according to the height of the conductive pillar 210 at the corresponding position. In some embodiments, before grinding once, the height of the conductive pillar 210 in the edge area Z1 of the surface of the wafer 100 is greater than the height of the conductive pillar 210 in other areas, then the pressure applied to the edge area Z1 of the wafer 100 during grinding is greater than the pressure applied to other areas. For example, Figure 1 As shown in , the height of the conductive pillar 210 at the edge of the wafer 100 is greater than the height of the conductive pillar at other positions, so the pressure at the edge of the surface of the wafer 100 is set to be greater than the pressure at other positions. In some embodiments, if the pressure at the edge of the wafer 100 is set to be greater than the pressure at other areas, the grinding time of two grindings by the soft grinding pad during one grinding can be different, specifically, the grinding time of the first grinding time is greater than the grinding time of the second grinding time.

[0028] The present invention optimizes the front-end process of a single grinding, so that the exposure state of the conductive column becomes more uniform. Specifically, the area where the middle conductive column is relatively low is raised, and the conductive column in the edge area is lowered, so as to ensure that when the wafer reaches the arrival stage, the total thickness deviation of the height of the conductive column exposed on the surface of the wafer is strictly controlled as a key characteristic, and can be controlled within a very small range, fundamentally solving the problem of inconsistent height of the conductive column. In addition, in the grinding process, the present invention sets a more reasonable process parameter formula. It covers a more optimized distribution method for parameters such as rotation speed, pressure, and grinding liquid flow, so as to ensure the efficiency and accuracy of the grinding process.

[0029] In some embodiments, the process of performing secondary grinding on the conductive pillar after the primary grinding using the corresponding grinding pad and applying the corresponding rotation speed and pressure can be a conventional grinding process. The conventional process generally uses a soft grinding pad in combination with a hard grinding pad for grinding. For example, the conductive pillar 210 after the primary grinding can be secondary ground by sequentially using a soft grinding pad, a hard grinding pad, a hard grinding pad, and a soft grinding pad and applying the corresponding rotation speed and pressure. In some embodiments, the rotation speed and pressure applied when different grinding pads are used for secondary grinding are the same, and each time the corresponding grinding pad is used to grind the wafer, the pressure applied to the edge area Z1 of the wafer surface is greater than the pressure applied to other areas.

[0030] Accordingly, see Fig. 9 Some embodiments of the present invention also provide a wafer structure formed according to the above-mentioned grinding method, including: a wafer 100, wherein the wafer 100 has a plurality of through holes, wherein the through holes have conductive pillars 210, and the height of the conductive pillars 210 is consistent with the surface of the wafer 100. In some embodiments, the surface of the wafer 100 also has a silicon oxide layer 220, and the surface of the silicon oxide layer 220 also has a silicon nitride layer 230. In some embodiments, after secondary grinding, the height of the conductive pillars 210 and the surface of the wafer 100 are consistent, including the surface of the conductive pillars 210 and the surface of the silicon nitride layer 230 on the wafer 100 are consistent.

[0031] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A grinding method, characterized in that: include: Providing a wafer, wherein the wafer has a plurality of through holes, the wafer has a plurality of conductive pillars, and each of the conductive pillars fills the corresponding through hole; Using at least one soft grinding pad in sequence and applying corresponding rotation speed and pressure to grind the conductive pillars once, so that the heights of the plurality of conductive pillars are consistent; The conductive pillar after the first grinding is ground for a second time by using a corresponding grinding pad and applying a corresponding rotation speed and pressure, so that the height of the conductive pillar after the second grinding is consistent with that of the wafer surface.

2. The grinding method according to claim 1, characterized in that: The rotation speed and pressure at the corresponding position applied each time the soft grinding pad is used to grind the wafer during the first grinding are smaller than the rotation speed and pressure at the corresponding position applied each time the corresponding grinding pad is used to grind the wafer during the second grinding.

3. The grinding method according to claim 2, characterized in that: The grinding liquid flow rate when the soft grinding pad is used to grind the wafer each time during the first grinding is less than the grinding liquid flow rate when the corresponding grinding pad is used to grind the wafer each time during the second grinding, and the grinding time when the soft grinding pad is used to grind the wafer each time during the first grinding is greater than the grinding time when the corresponding grinding pad is used to grind the wafer each time during the second grinding.

4. The grinding method according to claim 1, characterized in that: The surface of the wafer also has a silicon oxide layer, the surface of the silicon oxide layer also has a silicon nitride layer, and the height of the conductive pillar and the surface of the wafer are consistent, including that the height of the conductive pillar and the surface of the silicon nitride layer on the wafer are consistent.

5. The grinding method according to claim 1, characterized in that: Using at least one soft grinding pad in sequence and applying corresponding rotation speed and pressure to grind the conductive pillar once comprises: The soft polishing pad and the soft polishing pad are used sequentially and a corresponding rotation speed and pressure are applied to each soft polishing pad to grind the conductive column once.

6. The grinding method according to claim 5, characterized in that: The rotation speed applied each time the soft polishing pad is used for grinding is the same, and pressure is applied to multiple areas from the inside to the outside of the wafer each time the soft polishing pad is used for grinding, and the pressure applied to different areas is adjusted according to the height of the conductive column at the corresponding position.

7. The grinding method according to claim 6, characterized in that: Before the first grinding, the height of the conductive pillars in the edge area of ​​the wafer surface is greater than the height of the conductive pillars in other areas. During the first grinding, the pressure applied to the edge area of ​​the wafer surface is greater than the pressure applied to other areas.

8. The grinding method according to claim 1, characterized in that: The secondary grinding of the conductive column after the primary grinding using the corresponding grinding pad and applying the corresponding speed and pressure includes: The conductive column after the first grinding is secondarily ground using a soft grinding pad, a hard grinding pad, a hard grinding pad, and a soft grinding pad in sequence and applying corresponding rotation speeds and pressures.

9. The grinding method according to claim 8, characterized in that: The rotation speed and pressure applied when grinding with different grinding pads during secondary grinding are the same, and each time the wafer is ground with the corresponding grinding pad, the pressure applied to the edge area of ​​the wafer surface is greater than the pressure applied to other areas.

10. The grinding method according to claim 1, characterized in that: The applied rotation speed is the relative rotation speed formed on the wafer by rotating the grinding head and the grinding pad, and the applied pressure is the corresponding pressure formed by the grinding head on different areas of the wafer from the inside to the outside.

11. A wafer structure formed by the grinding method according to any one of claims 1 to 10, characterized in that: include: A wafer having a plurality of through holes, wherein the through holes have conducting pillars, and the heights of the conducting pillars and the surface of the wafer are consistent.

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