Polishing method for semiconductor substrates

Abstract

The objective of this invention is to suppress DIC and LPD that occur when a semiconductor substrate is moved from one polishing machine to the next. The present invention provides a method for polishing a semiconductor substrate, wherein the semiconductor substrate is moved while the following steps are performed using a plurality of polishing machines: an polishing cloth attached to a polishing platform is brought into contact with the semiconductor substrate held by a polishing head; an polishing agent is dripped onto the polishing cloth, causing the semiconductor substrate to slide for polishing; during the polishing of the semiconductor substrate in the polishing machine, a first polishing agent is changed to a second polishing agent with a lower polishing rate than the first polishing agent; compared to polishing using the first polishing agent, polishing using the second polishing agent reduces at least one of the following: platform pressure, polishing head speed, and polishing platform speed.

Description

Technical Field

[0001] This invention relates to a method for polishing a semiconductor substrate. Prior Technology

[0002] Among the polishing methods consisting of a multi-stage polishing process that involves polishing a semiconductor substrate multiple times, various studies have been conducted on methods to address issues such as surface roughness (uneven haze) and DIC (Differential Interference Contrast) defects. For example, Patent Document 1 discloses a method for polishing silicon wafers, characterized in that it includes three or more polishing steps such as initial polishing, intermediate polishing, and fine polishing. In the initial polishing step of this polishing method, the following steps are performed: a first polishing step, in which the wafer is polished with an abrasive containing water-soluble polymers; a second polishing step, which is performed after the first polishing step, in which the wafer is coarsely polished with an abrasive not containing water-soluble polymers; and a third polishing step, which is performed after the second polishing step, in which the wafer is polished with an abrasive containing water-soluble polymers.

[0003] In addition, Patent Document 2 discloses a multi-stage grinding process, which consists of three stages: primary grinding, secondary grinding, and fine grinding. In the secondary grinding, which is the middle stage, the process is carried out in three stages: [1] grinding with an alkaline abrasive that does not contain water-soluble polymers → [2] rinsing grinding with an abrasive that contains water-soluble polymers → [3] rinsing grinding with an abrasive that contains water-soluble polymers with a higher molecular weight than the polymer in [2]. Patent document 3 discloses a configuration aimed at improving the surface shape quality of silicon wafers. In the rough grinding process before fine grinding, grinding is performed using a grinding fluid containing abrasive particles, followed by grinding with a grinding fluid without abrasive particles. [Previous Technical Documents] [Patent Literature]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-174393. [Patent Document 2] Japanese Patent Application Publication No. 2019-021719. [Patent Document 3] Japanese Patent Application Publication No. 2014-17524. Summary of the Invention

[0005] [The problem that the invention aims to solve] Furthermore, the disclosures of the aforementioned prior art documents are incorporated herein by reference. The following analysis was performed by the inventors.

[0006] Multi-stage polishing systems, exemplified by the previously known three-stage polishing, involve moving a semiconductor substrate between multiple polishing machines while progressively polishing it. Generally, the movement between these machines is controlled to take place over a certain amount of time. However, in rare cases, there may be a standby time before the movement begins. Sometimes, the movement time of the semiconductor substrate between the grinding machines may be longer. Furthermore, the moving time of this semiconductor substrate refers to the time from the end of the grinding process on the grinding machine to the beginning of the grinding process on the next grinding machine. The inventors have discovered that when the movement time of the semiconductor substrate increases, quality deterioration occurs at a high frequency, accompanied by the occurrence of DIC defects, etc. In particular, they have noticed that when the movement time of the semiconductor substrate becomes 15 seconds or more, the aforementioned situation occurs at a high frequency.

[0007] The reasons for longer travel times are influenced by a variety of factors and are difficult to generalize. Examples include setting a longer grinding time in the later-stage grinding machine and a time difference in the movement of the semiconductor substrate in the device configuration. The aforementioned DIC defect can occur even in grinding machines performing coarse grinding, even in grinding machines that are involved in multi-stage grinding processes. The abrasives used for coarse grinding are usually highly etchable and do not contain polymers to protect the surface of semiconductor substrates. Therefore, it is speculated that between the end of the polishing process and the transfer to the next polishing machine, localized etching occurred due to the polishing agent adhering to the semiconductor substrate, resulting in watermark-like defects that were detected as DIC defects and LPD (Light Point Defect) ≥55nm. Typically, in order to suppress the etchability of residual slurry on the polishing surface, a process (rinsing process) is sometimes performed to allow an appropriate amount of surfactant or surface protectant to flow through. However, when rinsing is performed outside the final polishing stage, time loss (time inhomogeneity) will occur locally on the semiconductor substrate when the surfactant or surface protectant is replaced by the polishing agent, and when the rinsing liquid adhering to the semiconductor substrate is replaced by the polishing agent at the beginning of the next polishing stage. As a result, it is speculated that localized etching produces watermark-like defects, which are detected as DIC defects and LPD (Light Point Defect) ≥ 55nm.

[0008] The purpose of this invention is to provide a method for polishing a semiconductor substrate in view of the above-mentioned problems, which can suppress DIC and LPD when the semiconductor substrate moves from one polishing station to the next polishing station.

[0009] [Methods used to solve problems] To solve the above-mentioned problems, the present invention provides a method for polishing a semiconductor substrate, in which the semiconductor substrate is moved while performing the following steps using a plurality of polishing machines: an polishing cloth attached to a polishing platform comes into contact with the semiconductor substrate held by a polishing head, and an polishing agent is dripped onto the polishing cloth, causing the semiconductor substrate to slide for polishing; during the polishing of the semiconductor substrate in the polishing machine, a first polishing agent is changed to a second polishing agent with a lower polishing rate than the first polishing agent; compared with polishing using the first polishing agent, polishing using the second polishing agent reduces at least one of the following: platform pressure, polishing head rotation rate, and polishing platform rotation rate.

[0010] The semiconductor substrate polishing method of the present invention involves changing the first polishing agent to a second polishing agent with a lower polishing rate during the polishing process of the semiconductor substrate in the polishing machine. This can suppress the first polishing agent residue on the surface of the semiconductor substrate and prevent the residual first polishing agent from locally etching the surface of the semiconductor substrate.

[0011] The semiconductor substrate polishing method of the present invention is preferably to change the first polishing agent to a second polishing agent with a lower polishing rate during the initial polishing in the aforementioned plurality of polishing machines. This is because the first polishing compound used in the initial polishing machine has higher etchability than the second polishing compound. From the time of polishing in the initial polishing machine until it is transferred to the next polishing machine, local etching will occur due to the polishing compound adhering to the semiconductor substrate, which increases the possibility of DIC and LPD ≥ 55nm.

[0012] The preferred method for polishing a semiconductor substrate in the present invention is that, during polishing in the aforementioned plurality of polishing machines, if the time for moving the semiconductor substrate to the next polishing machine is 15 seconds or more, then during the polishing of the semiconductor substrate in the aforementioned polishing machine, the first polishing agent is changed to a second polishing agent with a lower polishing rate than the first polishing agent. This is because when the movement time of the semiconductor substrate becomes more than 15 seconds, DIC and LPD ≥ 55nm will occur at a high frequency.

[0013] The semiconductor substrate polishing method of the present invention is preferably modified so that the polishing time of the semiconductor substrate with the aforementioned second polishing agent is set to 3 seconds or more. This is because the time required to switch from the first abrasive to the second abrasive is only 3 seconds or more, resulting in significant effectiveness.

[0014] In the semiconductor substrate polishing method of the present invention, the second polishing agent mentioned above is preferably the same as the polishing agent in the final polishing process in the aforementioned plurality of polishing machines. This is because by using the same abrasive as that used in the grinding machine in the later stages of the multi-stage grinding process, the second abrasive can be used by changing the operating conditions of the grinding device without making additional equipment investments.

[0015] In the semiconductor substrate polishing method of the present invention, the second polishing agent mentioned above is preferably a water-soluble polymer with a molecular weight of less than 100,000. Although the larger the molecular weight of water-soluble polymers, the greater the grinding rate, the larger the molecular weight, the easier it is for the polymers to aggregate, which may lead to defects on the surface of the semiconductor substrate.

[0016] [Invention Benefits] According to various aspects of the present invention, a method for polishing a semiconductor substrate can be provided, which can suppress DIC and LPD that occur when the semiconductor substrate is moved from one polishing machine to another. Simple Explanation of the Diagram

[0017] [Figure 1] is a schematic diagram of the grinding machine used in the grinding method for semiconductor substrates related to an embodiment of the present invention. [Figure 2] is a diagram showing the grinding conditions of the comparative example and the embodiment. [Figure 3] is a diagram showing the characteristics of the first abrasive and the second abrasive. [Figure 4] is a graph showing the measurement results of DIC of the second abrasive during various grinding times in the grinding machine A of the embodiment. [Figure 5] is a graph showing the measurement results of LPD ≥ 55nm for various grinding times of the second abrasive during grinding on the grinding machine A in the embodiment. [Figure 6] is a diagram showing the polishing conditions of a modified example of a polishing method for a semiconductor substrate related to an embodiment of the present invention. Implementation

[0018] The following description describes embodiments of the present invention with reference to the drawings. However, the present invention is not limited to the embodiments described below. Furthermore, in each drawing, the same or corresponding elements are appropriately given the same symbols. Moreover, it should be noted that the drawings are schematic, and the dimensional relationships and ratios of the elements may sometimes differ from reality. Even among the drawings, there are cases where the dimensional relationships and ratios differ from each other.

[0019] Figure 1 is a schematic diagram of the polishing machine used in the polishing method for a semiconductor substrate according to an embodiment of the present invention. The polishing method for a semiconductor substrate according to an embodiment of the present invention involves polishing the semiconductor substrate while moving it between multiple polishing machines, which is a multi-stage polishing process represented by so-called three-stage polishing. Therefore, the polishing equipment used in the polishing method of semiconductor substrate is shown in Figure 1, which consists of a plurality of polishing equipment 10A and polishing equipment 10B. Furthermore, although only two grinding machines 10A and 10B are shown in Figure 1, if it is three-stage grinding, then three grinding machines are used; if it is multi-stage grinding, then the number of grinding machines used corresponds to the number of grinding stages.

[0020] Grinding machine 10A and grinding machine 10B are respectively equipped with a grinding head 2, a grinding cloth 3, and a platform 4. In the grinding process of semiconductor substrate, the grinding cloth 3 attached to the grinding platform 4 comes into contact with the semiconductor substrate 1 held by the grinding head 2, and the grinding agent 5 is dripped onto the grinding cloth 3, so that the semiconductor substrate 1 slides to perform grinding.

[0021] Furthermore, in an embodiment of the present invention, during the polishing process of the semiconductor substrate in the polishing machine 10A and polishing machine 10B, the first polishing agent is changed to a second polishing agent with a lower polishing rate than the first polishing agent. Here, compared to grinding using the first abrasive, grinding using the second abrasive involves reducing at least one of the following: platform pressure, grinding head rotation speed, and grinding platform rotation speed.

[0022] Ideally, when changing from the first abrasive to the second abrasive, the platform pressure of the grinding device and the number of rotations of the grinding head or the number of rotations of the grinding platform should be reduced, or both should be reduced. In addition to using a second abrasive with a low grinding rate, the operating conditions should be set to minimize grinding efficiency. If the operating conditions are set to the same as when using the first abrasive or to conditions with higher grinding efficiency, for example, when using an abrasive with a finer particle size than the first abrasive, the heat generated will affect the surface roughness and DIC of the end face. Therefore, it is best to set the operating conditions to minimize grinding efficiency.

[0023] The specific operating conditions need to be adjusted according to the configuration of the device, but generally it involves adjusting the platform pressure, the number of rotations of the grinding head, the number of rotations of the grinding platform, and the grinding time.

[0024] Platform pressure is typically set to, for example, 100 hPa to 300 hPa, taking into account grinding efficiency and processing capacity. The pressure when switching to a second abrasive with a lower grinding rate than the first abrasive is set to be lower than the normal pressure when using the first abrasive. In this invention, it is preferable to use as little polishing material as possible from the second polishing agent, and to set the pressure to a level that can wash away the first polishing agent adhering to the semiconductor substrate, typically set to 30 hPa to 80 hPa.

[0025] The rotation speed of the grinding head and the rotation speed of the grinding platform are usually set to, for example, 80 rpm to 150 rpm, taking into account grinding efficiency and processing capacity. When switching to a second abrasive with a lower grinding rate than the first abrasive, the number of rotations of the grinding head and the number of rotations of the grinding platform are set to be the same as or lower than the normal rotation rate when using the first abrasive. In this invention, it is preferable that the amount of abrasive produced by the second abrasive is as small as possible, and the rotation speed is set to the extent that the first abrasive adhering to the silicon wafer can be washed away, typically set to 20 rpm to 80 rpm.

[0026] The first polishing compound is the polishing compound used in general polishing, and can be appropriately selected from well-known polishing compounds without particular restrictions. In addition, the first polishing compound is different from the second polishing compound, and is preferably an polishing compound that does not contain polymers used to protect the surface of the semiconductor substrate. The second polishing compound uses a polishing compound with a lower polishing rate than the first polishing compound. If the polishing conditions are the same except for the polishing compound, the polishing rate is measured by the thickness of the center of the semiconductor substrate before and after processing using a flatness measuring instrument, and the difference in thickness is used as an indicator. In addition, the second polishing compound is different from the first polishing compound, and it is preferable to use a polishing compound containing a water-soluble polymer to protect the surface of the semiconductor substrate.

[0027] The free abrasive particles contained in the abrasive are preferably made of common silica particles. In terms of the concentration of abrasive particles in the abrasive, the lower the concentration, the lower the grinding rate.

[0028] The polymers used as abrasives are typically water-soluble, with hydroxyethyl cellulose (HEC) being preferred. Higher concentrations of water-soluble polymers result in lower grinding rates.

[0029] The larger the molecular weight of a water-soluble polymer, the greater the grinding rate. On the other hand, the larger the molecular weight, the easier it is for the polymer to aggregate, which may lead to defects on the surface of the semiconductor substrate. Therefore, in this invention, the molecular weight of the water-soluble polymer is preferably below 100,000. Conversely, the smaller the molecular weight, the lower the grinding rate. Therefore, in this invention, a smaller molecular weight is preferred. However, if the molecular weight is, for example, below 1,000, it may impair the protection of the wafer surface.

[0030] The second abrasive should preferably be the same as the abrasive used in the grinding process performed in the subsequent grinding stages (ideally the same as the abrasive used in the final grinding stage). When using a new abrasive as a second abrasive in addition to the abrasives used in the previous multi-stage grinding process, the cost increases because a dedicated piping and storage tank must be set up. By using the same abrasive as that used in the later stages of a multi-stage grinding process with a relatively low grinding rate, a second abrasive can be used without additional equipment investment by changing the operating conditions of the grinding equipment.

[0031] The polishing time of the semiconductor substrate when changing to the second polishing agent is adjusted appropriately according to the platform pressure, rotation speed, and even the slurry flow rate. The polishing time for semiconductor substrates when changing to the second polishing agent can be determined by confirming the amount of DIC reduction in advance and making adjustments. It can usually be set to more than 1 second, and it is better to set it to more than 3 seconds. When the polishing time of the semiconductor substrate is changed to 3 seconds or more when the second polishing agent is used, the occurrence of DIC and LPD can be suppressed more effectively.

[0032] Although the polishing method for semiconductor substrates in this embodiment can be applied to so-called three-stage polishing, it is not limited to three stages. It can also be applied to, for example, two to ten stages, regardless of the number of stages on the polishing machine. The grinding process using the second abrasive is excluded from the final stage of the grinding machine and is suitable for use in grinding machines where the movement time of the semiconductor substrate to the next grinding machine is 15 seconds or more.

[0033] Typically, the time it takes for a semiconductor substrate to move between grinding machines is less than 10 seconds. The reasons for the increased movement time include not only setting a longer grinding time in the subsequent grinding machine, but also the time difference that occurs during the movement of the semiconductor substrate due to the configuration of the device. The semiconductor substrate polishing method of this embodiment is preferably applicable to situations where the movement time of moving the semiconductor substrate to the next polishing station is 15 seconds or more during polishing in multiple polishing stations, especially when the substrate movement time of moving the semiconductor substrate from one polishing station to the next polishing station is 15 seconds or more, thereby suppressing the occurrence of DIC and LPD at a high frequency. When the time for a semiconductor substrate to move between the polishing machines is set to, for example, less than 10 seconds, if, for some reason as mentioned above, there is a possibility that the moving time exceeds the set time, the polishing method of the semiconductor substrate of the present invention can be used. Even if the moving time suddenly becomes, for example, more than 15 seconds, the occurrence of DIC and LPD can be suppressed at a high frequency.

[0034] The grinding of the second abrasive is preferably carried out in the grinding of multiple grinding machines (multiple grinding processes), and the initial coarse grinding (initial grinding process) is carried out in the grinding machine. Early grinding machines used highly etchable abrasives that did not contain polymers (water-soluble polymers) that were used to protect the surface of semiconductor substrates. Therefore, after grinding in the initial grinding machine and between being transferred to the next grinding machine, the semiconductor substrate may be affected by the abrasive adhering to it, resulting in localized etching and a high probability of DIC and LPD ≥ 55nm. That is, when the first abrasive is changed to a second abrasive with a lower grinding rate than the first abrasive in this invention, it is preferable that the first abrasive is an abrasive that does not contain water-soluble polymers, while the second abrasive is an abrasive that contains water-soluble polymers.

[0035] In the semiconductor substrate polishing method of this embodiment, the polishing cloth attached to the polishing platform in the polishing machine can be a conventionally known polishing cloth. When using polyurethane or other abrasive cloths such as non-woven fabrics, suede is preferred in this invention, considering the potential for deterioration in surface roughness. Chamois leather abrasive cloths are generally used for fine abrasive grinding. Compared to polyurethane or nonwoven abrasive cloths, they are softer and can achieve good surface roughness. Therefore, chamois leather type nonwoven cloths can be appropriately used in this invention.

[0036] In the semiconductor substrate polishing method of the present invention, it is preferable that the polishing agent used in the final polishing machine of the multi-stage polishing process is the polishing agent with the lowest polishing rate in the entire multi-stage polishing process, and after treatment with the polishing agent, a rinsing liquid is used to perform a rinsing process on the same polishing machine. The rinsing process can use known methods and rinsing fluids, for example, the grinding time can be set to 1 to 30 seconds, the platform pressure to 30 hPa to 100 hPa, and the grinding head rotation rate and the grinding platform rotation rate can each be 20 rpm to 100 rpm.

[0037] [Efficacy Test Results] Ten silicon wafers were subjected to multi-stage polishing under the polishing conditions of the comparative example and the embodiment described in Figures 2 and 3. In addition, Figure 2 is a diagram showing the polishing conditions of the comparative example (conventional conditions) and the embodiment, and Figure 3 is a diagram showing the characteristics of the first polishing agent and the second polishing agent. Therefore, using abrasive X (first abrasive) and abrasive Y (second abrasive) as shown in Figure 3, a three-stage grinding process (A, B, C) is performed. The movement time from grinding machine A to grinding machine B is set to 15 to 50 seconds, and the movement time from grinding machine B to grinding machine C is set to 10 seconds. In addition, the grinding time, platform pressure, head rotation speed, and platform rotation speed are shown in Figure 2. After grinding in the comparative example (after grinding using grinding machine C), DIC and LPD ≥ 55 nm were measured, and the relationship between the results is shown in Figures 4 and 5. Furthermore, in the grinding performed using grinding machine A in the embodiment, the grinding time using the second abrasive was varied (from 1 second to 50 seconds), and the relationship between the measured DIC and LPD ≥ 55 nm after grinding (after grinding using grinding machine C) is shown in Figures 4 and 5.

[0038] As shown in Figures 4 and 5, when the grinding time using the second abrasive is set to 3 seconds or more, the DIC and LPD (≥55nm) are significantly reduced compared to the comparative example. Even when the grinding time is 1 second or 2 seconds, the DIC and LPD (≥55nm) are also reduced compared to the comparative example, but the effect is particularly significant when the grinding time is set to 3 seconds or more.

[0039] The reason why the effect is significant when the grinding time of the second abrasive is more than 3 seconds is believed to be that as long as the time required to replace the first abrasive with the second abrasive is more than 3 seconds, it is sufficient. On the other hand, when the polishing time using the second polishing agent is less than 3 seconds, it is considered that the replacement of the first polishing agent with the second polishing agent is insufficient. As a result, the residual first polishing agent will locally etch the surface of the semiconductor substrate, resulting in DIC and LPD ≥ 55nm.

[0040] [Variation Example] Figure 6 is a diagram showing the polishing conditions of a modified example of the polishing method for a semiconductor substrate related to an embodiment of the present invention. As shown in Figure 6, in the modified example of the polishing method for a semiconductor substrate related to an embodiment of the present invention, polishing is performed while moving the semiconductor substrate in the order of polishing machine A, polishing machine B, polishing machine C, and polishing machine D. Here, the time for the semiconductor substrate to move from polishing machine A to polishing machine B and the time for the semiconductor substrate to move from polishing machine B to polishing machine C are 15 seconds to 50 seconds. Therefore, not only is the first polishing agent X changed to the second polishing agent Y with a lower polishing rate during the polishing of the semiconductor substrate in polishing machine A, but the first polishing agent X is also changed to the second polishing agent Y with a lower polishing rate during the polishing of the semiconductor substrate in polishing machine B. In this way, DIC and LPD ≥ 55nm can be suppressed by the localized etching of the semiconductor substrate surface by the first abrasive X.

[0041] Within the overall framework of this invention (including the scope of the patent application), modifications and adjustments can be made to the implementation forms and even the embodiments based on the basic technical ideas of this invention. Furthermore, within the overall framework of this invention, various combinations and even selections (including partial deletions) of various disclosure elements (including elements of each claim, each embodiment, and even each example, and elements of each drawing) are also possible. That is, the present invention may, of course, follow the overall disclosure and technical concept that includes the scope of the patent application and include various modifications and alterations that can be achieved by those with ordinary knowledge in the technical field to which the invention pertains. In particular, the numerical ranges described in this specification should be interpreted as meaning that any numerical value or subrange contained within such range is specifically described in this specification, even if not otherwise stated. Furthermore, the disclosures in the aforementioned cited documents may be used as part of the disclosures of this invention, and any combination of part or all of them with the contents described in this specification shall also be considered as included in the disclosures of this case.

[0042] 10A, 10B: Grinding machine platform 1: Semiconductor substrate 2: Grinding head 3: Abrasive cloth 4: Platform 5: Abrasive

Claims

1. A method for polishing a semiconductor substrate, comprising moving the semiconductor substrate while performing the following steps using a plurality of polishing machines: applying an polishing cloth attached to a polishing platform to the semiconductor substrate held by a polishing head, and dripping an polishing agent onto the polishing cloth to allow the semiconductor substrate to slide for polishing; during the polishing of the semiconductor substrate in the polishing machine, changing from a first polishing agent to a second polishing agent with a lower polishing rate than the first polishing agent; and reducing at least one of the platform pressure, polishing head speed, and polishing platform speed compared to polishing using the first polishing agent.

2. The method for polishing a semiconductor substrate as described in claim 1, wherein, during the initial polishing process in one of the plurality of polishing machines, the first polishing agent is changed to a second polishing agent with a lower polishing rate than the first polishing agent.

3. In the semiconductor substrate polishing method described in claim 1, if the time for moving the semiconductor substrate to the next polishing machine is 15 seconds or more during polishing in the aforementioned plurality of polishing machines, the polishing agent is changed from the first polishing agent to a second polishing agent with a lower polishing rate than the first polishing agent.

4. The method for polishing a semiconductor substrate as described in claim 1, wherein the polishing time of the semiconductor substrate using the aforementioned second polishing agent is changed to 3 seconds or more.

5. The polishing method for a semiconductor substrate as described in claim 1, wherein the aforementioned second polishing agent is the same as the polishing agent used in the final polishing process of the aforementioned plurality of polishing machines.

6. The polishing method for a semiconductor substrate as described in claim 1, wherein the aforementioned second polishing agent comprises a water-soluble polymer with a molecular weight of less than 100,000.

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